Chara forces Frisk into a realationship with her. Frisk is male. Chara is female. This is mature content it includes: violence, eventual smut and etc.

At night, Frisk feels a familiar presence. (Frisk x Chara) [Gender neutral Frisk and Chara]

Frisk saves Chara and Asriel, but when they return to the surface Frisk has a lot of trouble.

In your defense, the movies make possessing someone seem much easier. Rated T for implied child abuse and suicide. A look at Chara and Frisk learning to cope with being stuck together. Charisk.