Let's go:

I have a question though, I understand that all the dogs in Undertale are related in some way, but what are their exact relationships?

I assumed Dogamy and Dogaressa were like the mom and the dad, but it doesn't seem to be the case.

Then I thought maybe Endogeny gave birth to them, but I also found out Endogeny is like multiple dog monsters fused together.

Are the ones fused into Endogeny related too?

Are Dogamy and Dogaressa in an incestuous relationship if that's the case.

I NEED ANSWERS!

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It seemed to be an average day in Snowdin Town.

The monsters were going about their business, and you, well right now you were scolding a member of your family.

Right now you were at Doggo's station and the pajama wearing dog was sweating nervously as he stood before you.

"Are you smoking Dog biscuits again?" You asked your arms crossed giving him a disappointed look.

"N-no...Doggo stuttered hiding something behind his back.

"I can smell your breath." You said narrowing your eyes making Doggo sweat even more.

"Y-your nose is broken." He stuttered a bit more.

"Show me your hands." You demanded and he complied to reveal in both his hands he held nothing.

"Hmm." You pondered before sighing.

You then stiffened your entire body, you stopped moving every muscle, you were as still as a statue.

"(Y/N)?" Doggo asked looking around in confusion. "Where'd you go?"

He looked around a bit more and gave a sigh of relief.

He then revealed he was holding a few dog biscuits with his tail and he brought out a light.

Doggo gained a grin and began lighting the biscuits.

Suddenly you grabbed his wrist which made him flinch.

"Nuh uh boy." You stated with a flat look.

Doggo just sighed. "I don't know why I keep trying."

"I don't know why you keep smoking dog biscuits instead of eating them." You replied.

"I can stop whenever I want." He insisted before giving you a look. "Just not now."

"Hand over the lighter." You demanded and he groaned in response before handing you the object.

"Please quit it before it becomes an addiction." You said and Doggo's ears sagged.

"I'll try." The nearly blind canine sighed.

"That's all I ask." You stated putting the lighter away.

"(Y/N)!" Came a sudden loud voice that made both you and Doggo flinch.

You and your relitave turned to see a tall skeleton monster approach.

Papyrus:

"Oh hey Papyrus, how are you?" You asked with a smile.

"AS ALWAYS (Y/N), I AM AMAZING!" He replied in his usual bombastic and loud voice.

"Good to hear, do you need anything?" You asked.

"INDEED, I WOULD LIKE YOU TO COME AND MOTIVATE MY LAZYBONES OF A BROTHER!" He stated with a bit of annoyance in his voice. "IT HAS BEEN EIGHT SINCE HE LAST RECALIBRATED THE PUZZLES!"

"Papyrus, we both know me saying anything isn't gonna help much." You stated and Doggo nodded.

"Your big brother would win gold in the Olympics if laziness was a sport." Your relitave chuckled. "Actually I think he'd be too lazy to even show up for the event."

You gave him a flat look and replied:

"A few seconds ago you were smoking biscuits, I don't think you're in any position to judge someone." You reminded your relitave.

His ears sagged in sadness at that very true statement.

"THAT MAY BE SO, BUT AS CAPTAIN OF THE ROYAL GUARD YOU MUST CONTINUE TO TRY AND MOTIVATE THOSE WHO FOLLOW YOU!" Papyrus stated. "EVEN THE LAZY ONES!"

It was times like this you would wonder how a skeleton of all things could be so lively.

"Alright I'll try, but I make no promises." You shrugged.

"EXCELLENT, FOLLOW ME!" Papyrus yelled before running towards the entrance of the ruins where his older brother most likely was.

You began to follow leaving Doggo alone.

He suddenly pulled out a spare lighter and more dog biscuits.

He gazed at his items for a few seconds before sighing and putting the lighter away and simply eating the dog biscuits.

Later:

Both you and Papyrus finally made it to your destination where you saw the his elder brother.

Sans:

Plus what you would most likely call "a conveniently shaped lamp."

Immediately you picked up the scent of a human behind that lamp and stared at Sans who winked and you nodded.

"sup bro." Sans greeted.

"YOU KNOW WHAT'S UP BROTHER!" Papyrus said angry and annoyed. "IT'S BEEN EIGHT DAYS AND YOU STILL HAVEN'T RECALIBRATED YOUR PUZZLES!"

Sans just stood there with his signature smile as Papyrus continued his rant.

"YOU JUST STAY OUTSIDE YOUR STATION, WHAT ARE YOU EVEN DOING!?" The taller skeleton asked.

"staring at this lamp." Sans replied calmly.

"It is a cool lamp." You added Crossing your arms.

"i know right, hey paps, ya wanna look at it?" Sans asked and this annoyed Papyrus even more.

"NO, I DO NOT HAVE TIME FOR THAT!" He yelled stomping his foot. "I WANT TO BE READY WHEN A HUMAN SHOWS UP!"

"How do you prepare for that?" You asked with a raised brow.

"UH..." Papyrus said unable to come up with an answer.

"maybe this lamp will help you come up with an answer." Sans offered and that returned Papyrus to his angry state.

"SANS YOU ARE NOT HELPING YOU LAZYBONES!" He yelled.

"hey take it easy, i've gotten a ton of work done today." Sans defended himself. "a skele-ton."

"SANS!!!" Papyrus yelled.

You rolled your eyes at Sans' pun and decided to tease Papyrus as well.

"Come on you're smiling." You said poking his cheek bones.

"I AM AND I HATE IT, HIS RIMSHOT INTERRUPTED ME!" He yelled and you were sure if he had lips he'd be pouting right now. "WHY DOES SOMEONE AS GREAT AS ME HAVE TO WORK SO HARD TO GET SOME RECOGNITION!"

"wow, sounds like you're really working yourself...down to the bone." Sans said with a wink.

You let out a sigh and placed a hand on Papyrus' shoulder to calm him down.

"Okay Papyrus, let me try and talk to him, you just go and check on the puzzles." You said and the skeleton let out a sigh.

"VERY WELL, GET HIM TO PUT A LITTLE BACKBONE IN HIS WORK!" Papyrus said before letting out a loud laugh as he walked away.

"NYEH HEH HEH HEH HEH HEH..."

As his nyehs faded into the distance you turned your attention to the conveniently shaped lamp and said.

"Alright kid, you can come out now, I promise I won't hurt you." You assured and hesitantly a human child stepped from behind the lamp.

You walked up to the child and they seemed intimidated by your large size.

You kneeled down and gave them a pat on the head which calmed them down a bit.

"I take it you're going to try and leave the underground?" You asked and they nodded.

"Alright, you may pass but be careful okay?" You requested before rising and walking towards the ruin entrance.

The child watched you curiously but their attention was brought back to Sans who said:

"you don't have to worry about him kid, he's an honest guy, if he says he won't hurt you then he's not gonna." The Skeleton assured.

With that the two continued with a new conversation.

Meanwhile you reached the entrance of the ruins and stood before the giant purple door.

You placed a hand on the and asked: "Tori, are you there?"

"Yes." Replied a female's voice. "I assume you met them just now."

"Yes and like before I'll do my best to make sure they're safe." You said sounding a bit sad.

Toriel sensed this.

"If you're blaming yourself for the others, please don't." She spoke in an understanding tone. "I know you did your best to protect them."

"I promise, this time I'll keep them safe, I cannot afford to fail this time." You said clenching your fist.

"This child is different though, they are strong, I think things will end better this time I'm sure of it." Toriel said this time with a bit more enthusiasm.

"Did you two fight?" You asked surprised.

"Yes, but don't worry none of us are hurt." She assured and you let out a relieved sigh.

"That's a relief."

In response Toriel giggled:

"I still think it's funny how concerned you are for the safety of others and yet neglect your own."

That response was met with silence.

"You were always like that weren't you?" She asked. "Even all the way back in school."

You smiled a little as memories of your adventures in school returned to you.

"I can't even count how many times I had to patch you up or get you out of trouble." Toriel continued reminiscing.

"You didn't have to help me out you know." You said with a light chuckle. "But I still appreciate that you did."

"Of course I helped, you're my friend." She said sincerely.

You both felt a wave of nostalgia talking about a much simpler time the both of you shared.

Before all this happened.
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And there's the first chapter completed.

The next chapter is basically gonna be a flashback of everyone in the underground when they were younger.

It'll show some of the shenanigans you got up to, the bonds you formed stuff like that.

Throughout the story there's gonna be chapters like that