After charas death and toriel burying her with the other child souls that died a few years passed and due to being buried in the magical infused soil of the underground in mount ebott one day chara burst out of the ground scared and confused as she had lost her memory as she looked at herself she was reborn as a skeleton monster she started crying scared and Gaster had been roaming around on a walk after some work in his lab he heard the crying and was shocked but also fascinated to see her so what did Gaster do? Adopt her without letting Asgore or toriel know of course and become a single father to help and study her slightly.

You can be whoever you want to be to interact with them. And oc, other scientist, another monster, human, be gasters wife;3, and so on have fun