SoulTwist hasn't been fully developed yet so sorry if some things are off or unanswered.

Characters

-Frisk (Gaster & Frisk- personally i like to call them W.D. Frisk)

-Sans (Sans & Chara)

-Papyrus (Papyrus & Flowey)

-[Will be finished... Eventually.]

Storyline

About W.D. Frisk:

-I originally was going to combine them with monster kid, but accidentally combined them with gaster somehow, and.. The storyline started showing up in my head... Anyway. W.D. Frisk is(as you know) basically Gaster and Frisk. After some time(about 20+ years), "Frisk" showed up, and Gaster was deleted from his universe, but somehow managed to restore part of himself and took over Frisk's body partially so he could be the protagonist, and so he could see Sans and Papyrus. Gaster found out about some sort of parasite going around and infecting monsters, and wanted to make sure his "sons" were okay and would stay that way, but he was too late.

-Gaster considers Sans and Papyrus his sons since he adopted them. During the war of humans vs monsters, Gaster had found two skeletons that seemed to be small children. Gaster could obviously tell what had happened to their parents and decided to watch over and protect them.

Papyrus:

-Papyrus and Flowey, what a wonderful idea. A bold, confident and positive skeleton, uncertain about what's happening, since the evil flower drowns him in darkness and mental corruption.

Sans:

-Sans and Chara, such difficult partners. One is a kind yet lazy, pun-loving skeleton. The other, a dead, demonic child that hates every living being...

seemingly, though all they want is to be loved.

Sans is his own person, though Chara tends to take control whenever their so-called "Determination" overrides Sans'.

I'll edit this eventually, as i said above. If you have any questions or suggestions, feel free to say so in the comments.