After Varvatos Vex found out that the only way to power the cannon is the royal cores, he had to make a decision on whether to use the king and queen cores to kill Morando or let the universe die. Fortunately the royal siblings stop him despite that they were enraged that Vex would sacrifice their parents after all the hard work to regenerate them.

Unable to forgive him even after he explain that its the only way. However, they come up with another idea in which to use the wormhole to bring in the Akiridion fleet to face Morando as we now see Krel is contacting Zadra to gather the scientists and work on another wormhole from their side.

Krel: Lieutenant Zadra, we need you to listen very carefully.

Zadra: [I'm somewhat in the middle of a revolution here. Morando's absence has left his forces vulnerable to attack. We'll never get a better chance to retake the planet.]

Aja: Morando's activated Gaylen's core on Earth, and we need your help to stop him.

Krel: I'm sending you the specs for my wormhole generator. Gather the engineers and have them create a much larger version of my prototype.

Zadra: [How much larger?]

Krel: Big enough for the Akiridion fleet and some Foo-Foo reinforcements. (Chuckles.)

Zadra: [The bounty hunters that look like rabbits? Mm It will be done, my liege.]

Aja: This could really work, little brother.

Krel: Like you said, it has to, or we lose them all over again.

Aja: If it comes to that we will power the cannon with our own cores. Akiridion needs a king and queen.

Krel: I'll work with the engineers.

Aja: I'll help our friends defend our new home.

Vex: My liege, let Varvatos help.-

Aja stops him by pointing her serrator blade at him since she still cannot trust him at the moment.

Aja: You are ordered to stay and ensure no harm comes to our parents. No harm!

Vex: But the battle rages outside!

Aja: When this is over, I will decide what to do with you! If the worst comes to pass, be ready with the cannon.

Back in the battle, the Trollhunters and Creepslayerz are still fighting off the omens and Kubritz as we see the Creepslayerz got the omens limbs.

Eli: Legs! Got the legs!

The omen arm tries to punch Steve who's bashing it to the ground.

Steve: (Scream.) Die, creeper!

YN: Bring it over here!

YN is shoving one of the omen in a large puddle of lava to met its metal as the Creepslayerz toss the limbs in the lava.

YN: Now try rebuilding from that, tin cans.

He then pushes the Creepslayerz away before Aarg crashed near after fighting Kubritz.

YN: Go help Aarg. I got this one.

Steve: Got it.

They went to help Aarg before YN starts throwing rocks at her.

Kubritz starts blasting at the flying rocks before she charges a powerful blast at him. He created an earth wall to shield himself from the blast, but it wasn't enough. Only thing that protected him was his new heavy armor. Just before she could charge another blast, she was interrupted by Aja blasting her serrator at Kubritz before she joins YN.

Kubritz: Look around you. None of this would be happening if you and your brother had turned yourselves in like I asked!

Aja: You attacked our home!

Kubritz: This isn't your home, it's mine! And I made the bargain I needed to protect it.

YN: Oh like making a bargain with a guy who would literally destroy the planet?

Before they could even say anything, they feel the stomps coming close as everyone starts screaming while Toby is confused as he's floating with his hammer.

Toby: Hey, what's everyone looking at?

YN: Toby. Behind you!

Toby look back and saw its Morando. Only big and very dark along with traces of red.

Toby: Aah, what is that!?

Morando: Surrender the Tarrons to me.

Toby: Someone had a growth spurt.

Morando is about to squash Toby until YN throws his chain to catch and pull Toby away before Aarg catch him.

Toby: (Smiles.) Wingman! Always there.

Aarg: (Smiles.) Always.

However, Morando was actually releasing a laser blast that hit part of the city.

Aja: You call this protecting?

Kubritz: Morando will protect the Earth. He promised.

Aja: Whatever you think you were protecting Earth from, how could it possibly be worse than this?

Kubritz watch everybody starts running away from Morando.

Aja: It is never too late to do the right thing. Fight by my side. We can defeat him together.

Kubritz: This wasn't the deal.

YN: Enough with a god forsaken deal woman!

YN grabs Kubritz by her shoulder as he glares at her.

YN: Listen here, "Colonel". This is happening for two reasons. That giant guy is here and you're the one who allowed herself to be manipulated by him. And now we're trying to fix the chaos that you've brought on our home. So either you help us, or stay out if our way! Let's go, Aja. We got important things to deal with than her.

Aja: (Scoffs at Kubritz.) I feel sorry for you.

The couples run off to face Morando.

Aja: Morando, here I am!

Morando: Ah, the queen-in-waiting and her little human have finally decided to come out of hiding, I see.

Morando blasted laser at them but YN blocks it to protect Aja before the impact knocks him back a few feet away as he stood his ground despite that most of his armor pieces was torn apart. But that didn't stop Morando.

Morando: Goodbye, Princess.

Before Morando could do anything, he was interrupted by Kubritz blasting lasers at Morandos face.

Kubritz: Get away from her! You promised you'd protect my planet, not destroy it. I never should have trusted you.

YN: Wow, look who finally woke up in reality.

Aja: Better late than never.

Morando: You think I care? I'm a god!

Kubritz throws everything she go at Morando until he swings a punch at her where she crashed to the ground. Kubritz get back up, but she's stuck under the car as Aja come to help her out of the crash.

Kubritz: Finish him off. I weakened him. (Coughs.) It's never too late-

Morando fired a beam at Kubritz which the car exploded. After the cloud smoke is gone, Kubritz died in the battle while Morando is looking for princess Aja.

Morando: Where's the girl?

Aarg roars and attacks by jumping towards him. Unfortunately, Morando just yeeted Aarg away.

Toby: Wingman!

YN: Aarg!

Toby throws his hammer at Morando like Thor, but without looking, Morando caught it before glancing at the Trollhunters and the Creepslayerz.

Toby: Wow, good catch.

YN: Run!

They run away from Morando, but he's too big as he catches up to them. YN saw this and pushes his friends away with his earthbending to save them before he was grabbed by Morando.

Morando: Where is she?

YN: Like I'll ever tell the likes of you!

Morando: Aja Tarron, surrender yourself to me or your friend dies.

Morando squeeze the earthbender and his remain armor is about to crush him until Aja reveal herself.

Aja: Morando! Let him go.

Morando: If you insist.

Morando throw the earthbender up high and YN falls. He was about to brace himself for either the crash to the ground or crushed by Morando until Aja caught him thanks to her hover board as her hover board hit Morandos face.

Aja: I've got you!

YN: Now I feel a little embarrassed getting saved by a princess. (Smile.) But thanks.

They were then interrupted by a huge post sign nearly hit them by a foot.

YN: Hey, that almost hit us!

Toby: We need to get him out of Arcadia.

YN: Good call. Follow me!

They follow YN with their own fast travel. Aja with her hover board, Toby with his floating hammer, and YN with his earthbending. Morando pursue them while Aja contacts her brother.

Aja: Krel, are you there?

Krel: [One person at a time!]

Zadra and Krel are discussing their plan as all the foo-foo fighters are joining the fight while their scientist are making progress on the wormhole in their side. As they're discussing, the others arrived at the bridge of Arcadia as Morando follows them.

Toby: Why does everything end at the bridge? There's no production value, we're using the same location.

YN: Look on a bright side, at least no one else in Arcadia will get hurt.

Toby: What's the plan? Please tell me there's a plan.

Aja: We just have to keep him busy a little while longer.

Toby: That's your plan?

YN: I'm open for a better suggestions.

Aja: Don't worry, we'll improvise.

YN: Right behind you, Aja.

Aja charges at Morando with her serrator while YN uses lava bending to throw lava at Morandos feet and Toby uses his hammer. But it was not enough to stop a dark god.

Morando: Begone, nuisance!

One by one, Morando knocks them off the bridge. Luckily YN caught them both before they hit the ground.

Toby: He's too strong. He's stronger than Morgana.

YN: If Morgana has a weak spot, so does he. We just have to find it.

Aja: We'll never stop fighting you, Morando!

Morando: You will once you're dead.

Morando blasted both of his laser beams at them but Aja uses her serrator shield to block it.

But it couldn't last longer against the attacks.

Aja: I can't hold it any longer!

Suddenly Morando was stopped by Akiridion fleet who arrived thanks to the wormhole that's finished on time.

Morando: What? Impossible!

Aja: (Gasps.) It worked!

Toby: Yeah-heh-heh!

YN: Huh. This is just like "Earth Invaders".

The fleet focus on Morando while Zadra arrives with Krel on board so he can meet his sister.

Zadra: My liege, you and your brother should fight by each other's side.

Aja: Little brother, you did it!

Aja hugs her little brother before she speaks to Zadra.

Aja: Kubritz weakened him. We can take him down.

Soon a ship full of foo-foos arrive above Morando. Preparing to jump.

Foo-foo: This is my bounty!

2nd Foo-foo: No! My bounty! My bounty!

All the fuu-fuu jumps and starts hitting Morando as soon as they landed on him while Eli is helping with an Akiridion drone from his phone.

Zadra: He's vulnerable! Converge all attacks!

Everyone gives everything they got against Morando as its weakening him.

Krel: He's weakening!

Aja: We won't have to use Seklos's cannon after all.

Morando: Enough!

Morando then gathers enough energy to release a powerful attack.

YN: That don't look good!

Aja: Run!

They all run before Morando release an energy wave to destroy everyone as they all fall before a dust of clouds are everywhere. Fortunately most of them were distance enough to survived as we see Krel is looking for anyone alive.

Krel: Aja? Sister? Tobias? YN?

The ground then opens before the others climbed out with YNs earthbending.

Aja: Little brother?

Krel: Aja! Thank Gaylen, you're all right.

Aja: Thanks to YNs earthbending. But I wouldn't put it that way, exactly.

YN: That attack nearly took out the fleet and the fuu-fuu.

Krel: Morando is too powerful. The cannon is our only option.

Aja: We can't lose our parents, not again.

Krel: Father once told me that it's the choices we make in small moments that make things better or worse. But this isn't a small moment. It has to be us.

YN: There's gotta be another way.

Krel: We've tried everything and it wasn't enough to take down a god.

Aja thought about it to see if theres another way, but there wasn't any time for an alternative. So then she made a hard decision by contacting Varvatos.

Aja: Varvatos, we need Seklos's cannon.

Vex: [I know, my liege. We are already en route to you.]

We see Vex and Stuart are driving in the taco truck with the cannon and the king and queen who are still in the stasis pods.

Vex: Stuart, can't you go any faster?

Stuart accelerate as they're on their way to the planetarium until the omens are in their way.

Vex: Take evasive action!

The omens start firing before Stuart stop the truck and use it for cover.

Stuart: Oh, God!

Vex then contacts the royal siblings.

Vex: We have the cannon, but it has been waylaid by Morando's forces.

Aja: On our way.

Aja hangs the call before speaking to the humans.

Aja: Go back to town, make sure everyone's safe.

Toby: On it!

YN: Aja.

Aja: Yes?

YN: Just...please be careful.

Aja: You, too, my Earth boy!

Aja and Krel leave with Ajas hover board and made their way to the planetarium where Vex is defending Stuart who's preparing the cannon. Fortunately Zadra arrive to aid Vex to fight of the omens.

Stuart: Can anyone lend a hand?

Vex: Does Varvatos look busy right now?

Stuart: We are about to have a much bigger problem. And, yes, that's a pun.

One of the omen came from behind and is about to attack Stuart until Aja arrives and slice the machine in half.

Stuart: (Sigh in relief.) Oh. Be still, my six hearts.

Vex: We should hurry!

They all wasted no time to move the cannon together since its hard to move it  for a single person. Soon they made it to the planetarium where Morando is getting close.

Zadra: This is it!

Morando blasted lasers but Zadra uses her weapon to shield them from the blast. But it wasn't enough as it knocks them all back. Vex gets back up with his head ringing before he notice the king and queen are out of their pods.

Without any questions or hesitation, they made their way to the cannon while they hold hands as they know what's going on. Vex knows what theyre doing and he rush in and grabs Ajas serrator before shielding them with three force fields. Soon the royal siblings notice their parents are about to sacrifice their own cores to power up the cannon.

Aja: Mama? Papa?

They king and queen then charges the cannon by holding it where the cannon will power up before their children tries to stop them.

Aja: No! No, no, no!

Desperate they try to stop their parents when they just come back from stasis while Vex shields them all from Morando laser beam.

Krel: (Sob.) No!

Aja: (Sob.) No! Mama, Papa! This is our sacrifice to make. Let go. Let go!

Krel: You cannot do this!

The king and queen, however, comfort their children as this'll be their last moment together.

Coranda: Don't be sad, my children. Be proud. You have grown in love and strength beyond what your father and I could ever imagine.

Aja: (Sobs.) We can't lose you, not again.

Krel: (Sobs.)  Please, please, let us!

Fialkov: The fact that you are willing to sacrifice yourself for this world proves you are ready to take on this throne of ours, my son. Be brave, be true, and be kind to each other.

Morando: This ends now!

Vex: For the royals!

Aja: Varvatos!

Morando shattered the last shield and Vex got hit by the blast until the beam was then blocked before they see it was YN in his stone armor as he used all of the metal he has with him as a shield.

Surprising to see him here as hes protecting his the Akiridion friends with all he's got. Despite for arriving late, he holds his ground to shield them as long as possible.

YN: I can't hold it for long! Its now or never!

Failkov: We will always love you...

Coranda: My remarkable children...

With their last words, they sacrifice their cores to power up the cannon as its now ready to fire. YN fell on his knees as his metal is melted down. The Royal siblings wasted no time to raise the cannon and aim at Morando.

Aja: For Mama and Papa!

They press the firing button and blast it at Morando chest. Successfully and ending Morandos reign once and for all as he now all dusts. YN fell on one knee and yet kept his Balance.

Aja: YN!

YN: I'll live. Check on Varvatos, quick!

They all quickly check on Varvatos who's wounded badly from the blast.

Aja: No!

Vex: (Weak.) So, this is a glorious-

Krel: No, no, no. No, not like this, no! Hold on, Varvatos. Hold on.

Vex: My glorious warrior...I'm...I'm sorry.

Aja: (Sobs.) No, no. I-I'm not losing you. Forget a hero's death. You deserve a long and glorious life. I am your queen! And I order you not to die!

Vex close his eyes and they all begin to mourn their friends death until he speaks again.

Vex: Varvatos is yours to command, my liege.

Aja: (Smile.) Varvatos!

Zadra: Yes!

Stuart: You know, I think he's going to make it.

YN: Almost had me worried there. Not gonna lie.

Zadra: (To comms.) Izita, we require medical assistance.

Stuart: Oh, bellissima!

Stuart laughs and hugs Zadra who's close to him.

Zadra: No hugs.

Everyone celebrate as YN got a call from Toby.

YN: Toby, are you guys okay?

Toby: [Don't worry, everyone's fine.]

Everyone at the Arcadia celebrate their victory.

Toby: [Turns out Akiridions and those bunny dudes are real good at killing robots. Plus, they're super into Eli.]

YN: So it's over. Thank god.

Time skip

The next day, people of Arcadia are coming to the school for an special event where we see Toby is speaking to the audience.

Toby: I know you all came here tonight to see a totally awesomesauce sci-fi epic but first, Aja and Krel Tarron our friends, classmates and our real-life intergalactic heroes.

The audience applause while was hesitant to step in the stage.

Aja: (Whispers.) He said both of us, little brother.

Krel: (Whispers.) This is all you. Go.

Krel encouraged his sister. Enough for her to step in the stage and introduce herself before telling them a story of their journey from the beginning. She also reveal herself her Akiridion appearance and it made people excited. She also thanks them for welcoming her and her family to their world and they had a great adventures together that they won't forget. Afterwards, she introduce them a movie that Toby, Eli, and Steve have been working on before everyone watch it on screen known as Kleb or alive. While everyone's watching the film, Aja and YN are out of stage and have a conversation.

YN: Hey, I'm sorry about your parents.

Aja: (Sigh.) Thanks. I did thought about introduce them to you. If only Morando didn't have Gaylens core.

YN: Hey, I may not knew about my parents. But if there's one thing that I know about parents, is that no parents should outlive their own children and no sacrifice comes greater to save them. Trust me, my parents gave their lives to save my uncle and I when I was young.

They both hold each others hands.

YN: So, are you going back to Akiridion-5?

Aja: Yes, but you can come with. How would you like to be the first Earthen ambassador to Akiridion-5?

YN: I am honored, but I can't leave Arcadia unsafe. It needs its protector. At least until I know for certain they'll be safe. But I promise I will see you again.

Aja: Pinky promise?

Aja hold out her hand with her pinky, but YN gently hold her hand before crossing his heart.

YN: I cross my heart to it. Until my last heartbeat.

Aja: I understand. In the mean time, we will just do long distance. Very long distance, my earth boy.

They were about to kiss until Eli interrupt them.

Eli: I'll go, I'll go! I'll be the ambassador! Pick me, pick me!

Aja: What will you tell your parents?

Eli: That I'm studying abroad, in Cantaloupia.

YN: Sounds like a fair choice. Not sure if I'm fit to be an ambassador anyway.

They all laugh together as the film continues to play. Soon the Akiridion prepare to leave with the wormhole for transportation.

Lucy: Before we all go, snickerdoodles and trail mix for the journey.

Stuart: Oh, I'm gonna miss you kids so, so, so much. You gotta promise to transmit and email and call. Are postcards still a thing on Akiridion-5? If they are, send one.

Krel looks at Arcadia one more time until his sister arrives to meet him.

Krel: You were right, Aja. We made a lot of friends on this mudball.

Aja: Little brother...

Krel: All my friends are here. This is my home.

Aja: I-I know.

Aja understands, knowing that her little brother will stay on earth before Vex arrives.

Vex: The humans and this planet are lucky to have you.

Toby: Yes! DJ Kleb is staying in the house!

Humans cheers.

Ricky: Unpack the bags, Lucy. We're staying on the mudball, too.

Lucy: You can say that again!

Krel: (To Aja.) You'll be okay without me?

Aja: Of course. Now we will both be home.

Soon the wormhole opens for the Akiridion and the foo-foo while Vex is saying his goodbye to Nana.

Vex: Many moons from now, when Varvatos' bones groan, and his blood slows to a crawl, and he sees the twilight of his life, there would be no greater honor nothing more glorious for Vex than to have you by his side. But I am the royals' guardian and I must go back and stand by her side.

Nana: I know you can't stay, but is there oxygen up there?

Vex: There is, in abundance.

Nana: Then when Toby-pie leaves for college, make room for one more!

Vex: (Gasp excitedly.) You mean it?

Nana: Now kiss me, you big, blue lug!

The Akiridion begins to leave along with Eli. Just as Aja is about to join, YN stops her for a moment.

YN: Wait, Aja!

YN holds out a small present for Aja.

YN: I almost forgot to give this to you.

Aja: What is it?

Aja opens it and reveals a family stone figure of Aja and her family which surprised her.

YN: I um...made it myself. Thought to make it for you before you leave. So you wouldn't feel alone when you're ruling Akiridion-5.

Aja: (Smiles.) Their beautiful. Thanks, YN. I'll miss you.

YN: My too, my queen.

They kiss one last time before Luug but in and barks.

YN: (Chuckles.) I'll miss you too, buddy.

Aja: (Laugh.) Come here, boy!

YN pat Luugs head before Aja carry him and heads to the wormhole where Vex awaits.

Vex: After you, my queen.

Aja. About that I'll have to come up with my own title.

Vex: Glorious.

Aja look back to her friends and little brother one last time.

Toby: Why do these things always end in tearful goodbyes?

YN: That, my friend, is the most mysterious question.

Aja: Come on, Luug. We're going home.

With that, Aja heads back to Akiridion-5 and their journey is over. Soon nightfall came and we see Aarg, YN, Toby, and Steve are walking on the street to head back home.

Steve: Man, rest of this summer's gonna eat farts.

Toby: Yeah, it is kinda hard to top destroying an alien god.

YN: I still think fighting Gunmar was more of a challenge compare to the alien god.

Toby: I'm just glad we don't have to deal with gumm-gumms anymore.

Aarg: Wingman did good. Proud.

Steve: I'm gonna miss my Creep Slaying partner.

YN: I'm gonna miss Aja. But she has her duty as queen as we have ours as Trollhunters and Creepslayerz. Its just gonna be different now.

Toby: Yeah, I felt like that after Jim and Claire and everybody left on their quest.

Steve: Whoa, whoa, whoa, we're talking about my problems here, buttsnack.

Suddenly a cat appear in front of them.

Aarg: Cat. Yum.

Toby: Ooh! Hey, lil' guy! You lost?

Out of nowhere, the cat suddenly speaks as he's wearing glasses.

Archie: Beware. You, you are in grave danger.

Steve: Whoa! A cat with glasses!

Toby: The cat just talked and you're focused on its eyewear?

Steve: I've seen aliens, creeps and trolls, Domzalski.

YN: (Shrugs.) At this point, we shouldn't be surprised.

Steve: Yeah, and I'd like to know why the talking cat's wearing glasses.

Archie: Bad eyesight.

Aarg: Not cat, familiar.

YN: (Confuse.) Familiar?

Steve: (Laughs.) No way! I'd remember if I met a cat with glasses.

Aarg: No. Wizard assistant.

Archie: Assistant? That's very offensive. I am a wizard associate, thank you very much.

The cat then walks on two foot before leaving.

Archie: Now, come with me, or the worst will come to pass.

Steve: Hey, are you threatening me, pussycat?

Archie: No. I'm warning you. Put simply, the world as you know it is about to end. Meow.

With that warning, the cat runs off.

Toby: Wha...

Steve: Ah, not again!

YN: (Groans.) Screw this. Its passed my nap time.

-End of Book 4-