NinjaTale - Chara

In this AU Chara practically doesn’t differ from canon: she is also the first human who had fallen in the Underground, she was Toriel and Asgore’s adopted child and has died, that Asriel absorbed her soul, rose to the Surface, and the war between people and monsters started. But when Frisk fell in the Underground, Chara’s phantom installs in her body because of the one type of soul, so the protagonist would be like jinchūriki, if Chara was a tailed beast. She can take control of Frisk’s body (Frisk’s eyes become red, like Chara’s), do jutsu for her (especially in extremal situations when she understands, that the protagonist isn’t able to do anything), or she can allow Frisk use her chakra or heal her. But Chara doesn’t do this from the best of motives: she needs in Frisk like in the last human soul which is important to Asgore to destroy the barier, that monsters could rise to the Surface and start the war with people, who Chara hates (and Frisk too). She takes the control of the protagonist’s body and motivate battles, that Frisk will faster find her death. If Frisk is mentally stronger and doesn’t allow to take control of her, tries to get friends with Chara and find the hope in people again, Chara in particular uses her power to help her and heal. Despite Chara has very agressive intentions, she doesn’t start the Genocide: if protagonist starts the hunt on all the monsters, for Chara, observing Frisk’s cruelty and monsters’ despair, it is a very huge shock, like for the unhappy person, and she dissapoints not in people only, but in the whole world too, starts to get mad, takes an absolute control and decides to destroy the Underground.
And about Chara’s characteristics: her character is very difficult, thanks to the living on the Surface, even mad. She is nervous, haughty, sometimes cruel, but she isn’t black-hearted. Nevertheless her actions, she loves monsters, though she decides to sacrifice some of them for their sake, like she will tell Frisk. In the Ruins she doesn’t motivate the protagonist to fight with monsters because she doesn’t see any sense to spend her power there, but after getting out of there she can attack weak monsters as well as bosses for achievement of her purposes. She is as strong as Frisk is weak, very good at taijutsu and ninjutsu, but at genjutsu she is quite better. Chara is wearing clothes for an old style which was during her live and death.