Junko: Ah... sibling love is such a beautiful thing. Some siblings will do anything for their little sibling, right Mukuro?

Mukuro: Right. Even if that means trying to turn them back human after turning into something they never wanted to become. Like Tanjiro and Nezuko, the Kamado siblings of Demon Slayer.

Junko: As well as Edward and Alphonse, the Elric Brothers of Fullmetal Alchemist. 

Mukuro: The stage is set. We're Mukuro and Junko and-

Junko: Oh nobody cares about us, sis! They only care about the time!

Mukuro: The time?

Junko: That's right! Because it's time... it's time... it's time for a DEATH BATTLE!!!

Edward and Al were wandering around an abandoned factory.

Edward: Jeez, why do we gotta observe a dusty old place like this?

Alphonse: It can't be helped you know?

Edward: Yeah yeah I know... hm?

Edward looked up to see a demon running away.

Demon: AAAH! Someone help me!

Just then, Tanjiro came from above and cut the demon's head off with ease.

Edward: What the?! Hey! Did you kill that guy?!  That's freaking illegal!

Tanjiro: Hm? O-Oh! I'm sorry sir. I didn't know there was a child watching...

Edward: Geh... I'm sorry... you wanna say that again?

Alphonse: Brother... I think you should try and calm down...

Edward: Tch... even then, he definitely killed that man. You're gonna have to come with us.

Tanjiro: Huh? Um, this may be a misunderstanding! Plus, I can't exactly go with you at the moment.

Edward: Fine. If your gonna refuse... then we'll just make you!

Edward made a blade with his metal hand and dashed at Tanjiro. He swung the blade and Tanjiro blocked it with his sword. 

Tanjiro: (A metal blade from his hand? Is he a demon?)

He looked up to see Al jumping down at them. They both jumped back as Al got between them, creating a crater upon landing. Tanjiro dashed back at him and swung his sword, but Al blocked it with his arms. Edward went to strike Tanjiro from the side, but Tanjiro quickly jumped and blocked with his blade. He pushed Edward back and dashed at him.

Tanjiro: Water Breathing First Style... Water Surface Slice!

As swift as water, Tanjiro went for a swing of his sword and Edward jumped back to dodge it. As he did, Alphonse came from behind to grab him. The attempt failed as Nezuko came out of her box and kicked him back.

Edward: What the?! You keep a little girl locked in that thing?!

Tanjiro: W-Wait! It's not like that! She's my sister!

Edward dashed at him. They both swung their blades and clashed.

Edward: That's even worse!

As they were clashing blades, Nezuko was ready to intervene but Tanjiro spoke up.

Tanjiro: Nezuko! Handle the guy in armor! I got this!

She nodded and dashed after Alphonse, going for a kick. He blocked it and went for a punch but she shrunk in size to avoid getting hit. She then went back to her normal size and went for another kick that sent Alphonse flying into a wall. 

Alphonse: (What is this strength? This girl's stronger than I thought... is she a homunculus?)

Al started to get up and was ready to fight. Nezuko ran at him as Edward managed to push Tanjiro back. He quickly threw his jacket off, revealing his metal arm.  He clapped his hands together and onto the ground, causing giant fists to emerge and come at Tanjiro, who was cutting them all up and dashing at him. He quickly jumped into the air.

Tanjiro: (Second Style... Water Wheel!)

He went for a vertical slash and Edward blocked it with his metal arm.

Tanjiro: (His arm is tough... I may need to-)

Before he could think anymore, Edward quickly went to headbutt him, causing his own eyes to roll in the back of his head.

Edward: (So... hard...)

Tanjiro was knocked back, but ran at him and headbutt him back, causing Edward to stumble.

Edward: (Too... hard...)

Tanjiro then grabbed him by the shirt and went for a third headbutt that knocked Edward to the ground.

Edward: (His head is too goddamn hard!!!)

As Edward was down, Tanjiro went to hold up his sword.

Al was busy blocking Nezuko's kicks before he noticed them.

Alphonse: Brother!

He caught Nezuko by the leg to her surprise. He then threw her as hard as he could into Tanjiro as they were sent flying into the wall. Edward got up, holding his head.

Edward: Thanks, Al... 

Alphonse: No problem!

As Tanjiro looked down for the count, Edward dashed at him to try and finish him off. As soon as he did, Nezuko dropped down to intervene with a kick and Edward blocked it. He swung his blade and Nezuko dodged it, only getting grazed in the cheek as she kicked him into Alphonse, who quickly caught him and was knocked back a bit.

Alphonse: Are you okay?

Edward: Yeah... she's a tough one. 

Nezuko dashed at them and Edward quickly placed his hands on the ground, creating an earth wall to block her attack. She destroyed the wall with a single kick and the two brothers jumped back. Alphonse used the philosopher's stone and touched the wall behind him, creating five spears that launched at her. She quickly dodged them and ran at him. She jumped up and went for a kick but he dodged it. She turned and went for a flying kick and he ended up blocking it as he was knocked back. She went for a third kick but he caught it and she quickly used her other foot to kick his hand off her, but he quickly reacted and as soon as he let go, he grabbed her from behind tightly.

Alphonse: Now I got you!

Edward: Good thinking Al! Hold onto her!

Edward clapped his hands together as Tanjiro began to wake up. He saw Nezuko in danger.

Tanjiro: Nezuko!

As he began to get up, Edward saw him and placed his hands on the ground, summoning several cannons that were aimed at Tanjiro. 

Edward: Try and dodge this!

He fired several cannonballs at Tanjiro, who was cutting them while dashing at Edward.

Tanjiro: Sun Breathing... Dance!

As he got in close, he cut all the cannons with a single swing of his sword. 

Edward: What the?!

He went for another strike onto Edward, who hardened his arm and blocked it before getting knocked back.

Edward: (His fighting style suddenly got more aggressive!)

Tanjiro went for another strike, but Edward flipped back to dodge it. Tanjiro then stopped to take a deep breath and looked into the Transparent World. He could see the inside of Edward.

Tanjiro: (His arm and leg are gone... they must be replaced with that metal arm. And he's definitely not a demon... but that's not what concerns me.)

Edward swung the blade on his arm and Tanjiro swung his sword as they clashed. They went for another swing and clashed again before butting heads.

Tanjiro: (I'm more concerned about his friend.)

He glanced towards Alphone who was still holding onto Nezuko.

Tanjiro: (I can see through his armor, but there's nothing inside! Not just that... I can't smell him either... unless...)

Edward: Hey buddy! My eyes are up here!

Tanjiro turned back to Edward who punched him in the face and knocked him back. Nezuko saw this and tried to get out of Alphonse's grip. She couldn't smell him but assumed he must be a demon as she summoned flames to burn him.

Alphonse: Fire? Sorry, but that's not gonna work on me- huh?

Al started to struggle to keep his grip as Nezuko grew in size and got stronger. She grew a horn and leaf marks around her body as she took him and threw him into a pillar. He began to get up and Nezuko immediately trusted her claws. He went to dodge it but was too slow as Nezuko stabbed straight through his chest and into his body, but was surprised to find nothing there. Al then used both his fist to smash Nezuko to the ground. He used the philosopher's stone to make restraints that pinned Nezuko to the ground.

Alphonse: Sorry about this!

He then started punching Nezuko in the face over and over again, trying to knock her out. 

Tanjiro: Leave my sister alone!

Alphonse: Huh?

He looked up to see Tanjiro coming down on him.

Tanjiro: Raging Sun!

Tanjiro unleashed two burning slashes. The first one cut off Nezuko's restraints, freeing her. Al went to use his arm to block the second as it was cut clean off.

Tanjiro: (No blood! So I was right... that armor is his body!)

Al got back and used the philosopher's stone to regrow his arm as he picked up the one that was cut off and turned it into a sword. He went for three consecutive strikes but Tanjiro blocked them all. Meanwhile, Edward went to strike him from behind but Nezuko quickly got up and swatted him away like a fly. Tanjiro and Nezuko then stood back to back and as Edward and Al dashed towards them and Al thrust his sword as Nezuko and Tanjiro switched places. He managed to stab Nezuko in the chest, only for her to quickly react by punching him and knocking him away. She took the blade out of her chest and tossed it aside. 

Meanwhile, Edward made a spear from the ground and dashed at Tanjiro, thrusting it at him and Tanjiro quickly dodged it.

Tanjiro: Sunflower Thrust!

He thrust his sword and Edward dodged the attack before swinging his spear, but he only attacked an afterimage.

Edward: What?

Tanjiro: Fake Rainbow!

Edward looked back to see Tanjiro right behind him.

Tanjiro: Flame Chariot!

Edward quickly swung the blade on his metal arm as Tanjiro went for a leaping swing of his sword and they both clashed, knocking each other back. Edward quickly turned the blade on his metal hand into knuckles. Tanjiro went for another thrust from his blade and Edward dodged it before punching Tanjiro in the face and into a stone wall. 

Nezuko saw this as she was about to go help but Al got in her way.

Alphonse: Not so fast!

He went for a punch and Nezuko got back to dodge it. They then both went to punch each other and they clashed, causing a shockwave that pushed them both back. Alphonse then used the stone to make a bunch of spikes come up from the ground and stab Nezuko all over her body, lifting her p and pinning her into a wall. She struggled to move as Al looked up at her.

Alphonse: Sorry, you're gonna have to stay up there for a while.

He turned to see how his brother was doing.

As he did, he saw Tanjiro was starting to recover. Edward clapped his hands together and dashed at him.

Edward: (Alright! I'll have no choice but to tear him to shreds!)

He dashed at Tanjiro with an electrically charged hand as he went to try and grab his face... but Tanjiro quickly saw it coming.

Tanjiro: Burning Bones, Summer Sun!

Tanjiro went for a circular slash that cut Edward's metallic arm clean off.

Edward: GAH!!!

Alphonse: Brother!

Tanjiro looked up at him and saw the thread.

Tanjiro: I got you! Sun Breathing... Clear Blue Sky!

He went for a 360 sword swing, but before he could cut Edward, Alphonse knocked Edward back and took the slash himself, immediately getting cut in half vertically and dropping to the ground.

Edward: Al NO!!!

Tanjiro saw this and was almost surprised. He looked down at the empty suit of armor as he saw the seal in the back was cut in half.

Tanjiro: He sacrificed himself... to save his friend...

Edward fell to his knees and pounded his fist on the ground.

Edward: How could you... he was... my brother... HE WAS THE ONLY THING I HAD LEFT!!!

Tanjiro looked at Edward, then looked down as he felt bad for what he did.

Tanjiro: I... I see...

He then looked back at Edward and noticed he wasn't pounding his fist anymore... but it looked like he was drawing something.

Tanjiro: H-Hey-

Edward: Too late!

He stood to one knee and revealed a small transmutation circle. He placed his hand on it and summoned several large columns to try and squash the Demon Slayer. Tanjiro was surprised but quickly reacted as he jumped from column to column, dashing closer to Edward as he cut a few columns in half. Nezuko saw this as she slowly lifted her hand and gripped her fist.

Nezuko: (Blood Demon Art... Exploding Blood!)

 Suddenly, Tanjiro's blade burst into pink flames, and the color changed into a crimson red blade. He got in front of Edward and before he swung his sword he whispered.

Tanjiro: I'm sorry...

He cut Edward's head clean off and it fell to the ground with a tear in its eyes. Edward looked behind him at the two fallen brothers. He stabbed his blade into the ground and gave them a prayer in respect. He then looked up and noticed Nezuko had disappeared.

Tanjiro: Huh? Nezuko? Where'd you go?!

He turned and saw Nezuko poke her head out of her box before falling back asleep. He let out a peaceful smile, walked towards her, and pat her head.

Tanjiro: You fought well... now let's go home...

He picked the box up and walked away.

Junko: Well... that was way longer than we had planned.

Mukuro: Well, it wasn't as simple as we expected, that's for sure. In a one-on-one situation, the results could have very well been different.

Junko: Yeah, Erin could potentially kill Nezuko with his little Destruction Alchemy. But there was no way Tanjiro would let that happen. And with Alchemy, there was always the potential of overwhelming Tanjiro. But Nezuko could always power through it to protect Tanjiro.

Mukuro: Both teams scale to dodging lightning, but Tanjiro has already taken on faster opponents with the help of the Transparent World. And while he couldn't predict Al's moves using the Transparent World, he could easily do so with his sense of smell, which was great enough to help him predict the location of various traps and other objects.

Junko: And while the destruction alchemy could potentially kill Nezuko, it wasn't 100% guaranteed as it's never been shown to destroy one's body completely. Taking that into account, even if Tanjiro did die, they would have no real way of killing Nezuko. Especially considering that she's immune to the sun.

Mukuro: But with Alphonse's ability to repair himself using the philosopher's stone, couldn't the same be said for him? 

Junko: Not necessarily. Remember that even with the stone, Al becomes practically useless if his body takes too much damage. Also, it's totally obvious that the Elric Brothers need both their arms to perform their alchemy magic thingy. It wouldn't be surprising if Tanjiro found that out and simply cut their arms off before they made their next move. Whereas neither Nezuko nor himself have such an exploitable weakness.

Mukuro: That doesn't mean this match was completely one-sided. This battle could have easily gone either way. But more times than not, your winners are Tanjiro and Nezuko.

Winners: Tanjiro and Nezuko Kamado

+Can predict movements

+Can exploit weaknesses

+Better smell

+Breathing

+Nezuko is physically stronger

+Nezuko's healing factor

=Intellect

     -Minus Nezuko

=Speed

-More reckless

-Tanjiro isn't as strong

-Not as many hax

-Both have limits to their healing factors

Losers: Edward and Alphonse Elric

+More training experience

+Less reckless

+Alchemy

+Alphonse's Philosophers Stone

+More hax

+Edward could possibly kill Nezuko

=Intellect

    +Both smarter than Nezuko

=Speed

-More predictable

-Stone has its limits

-Automail limbs and Al's body can only take so much damage

-Edward's temper

Junko: Next time on Death Battle!

https://youtu.be/R9PK-OeogWw

Yang Xiao Long vs Akane Owari

(RWBY vs Danganronpa)