Chara had been watching the human ever since Frisk had fallen on her grave of flowers. Chara at first wanted to convince her to kill the humans and tried. But then Chara saw that this human went out of her way to try and save her brother.
Asriel, I'm so sorry about what I've done to you, I deserve to be trapped here in this darkness with only this human as company and the memories of the human taunting me.
Chara then went under the patch of light from the hole she fell into as an attempt to escape humanity, in one way or another. She had at first when she came here tried to pretend she was Frisk and tried to live Frisk's life, she then realized it was like watching TV, you can wish all you want but it can't be real.
Chara knew she could use the human for some uses, at first she saw it wrong but then she realized she could use Frisk to get back at the humans who made her life hell on the surface.
That was then. Now Chara thought the human needed peace, and that Frisk was beautiful? Am I seriously falling for the human, this is what got me beat up back on the surface, besides it must just be loneliness speaking.
It wasn't just loneliness. Chara had visited Frisk and talked with her showing herself every night after that one. Chara enjoyed spending time with Frisk overtime, exchanging stories like when Papyrus tried to solve the horoscope and whatnot. Chara wished to be human again, then she could spend more time with Frisk....... But Chara knew humanity would be the same as it ever was. 'Would it be worth it?' she asked herself. She didn't think so. She wasn't so sure Frisk even liked her back.
(Some of this chapter was written on the computer, btw screw the computer version)