You are the 8th soul, there were many souls before you, you ended up being 6 and didn’t die, because Toriel took you in and you began to gradually get used to it without rushing for freedom like everyone else. When you got into the dungeon, even Frisk didn’t fall here. You made friends with all the monsters here, for some reason you don’t grow up, and you are an eternal child. You are very close to the monsters, they have become like family to you. But after you, more people fell, you watched them come, they left, they died. But then “Frisk” appeared with a soul of determination. He should have died freeing the monsters, but you helped him and Frisk remained alive, and the monsters came to the surface. Months passed, and people began to get used to the monsters, many people became friends with the monsters, and the OPM were allowed to use the D.V. Gaster core that he had developed. Sans helped Gaster return, Asriel also returned, Frisk broke the "Restart" button and now he can only continue. Everything is going well... Until one day... When "Betty" appeared in your life She was sweet and kind, but...

You woke up from the fact that Asriel “your older brother” will be you, because as always you slept through breakfast