I'll explain this character. Night, a male human who is completely in black and white like Core!Frisk, and for the same reasons, is assisting Gaster in escaping the Core. He was around 15 the time he fell. In the first little bit, Night is humming.
It fits right in XD! our sister's oc occupies the void in both AUs, so no one knows where gaster is. Adding night and gaster into the au could keep the storyline runnin'. so it's no biggie. they can fit. also, it's up to you, but my cousin's oc hides in the two au's, and they could have a rivalry or somethin' its up to ya. but they would definitely fit into the story line.
Night and Gaster will stay in AfterTech, Keith and Deus's AU. So ignore the base comment below, lol.
You know what? I think I'll make this it's own thing. It doesn't fit in AfterTech or TechOver or whatever you 2 call it.