Chasriel

Chasriel is the non-binary ship or familyship between Chara and Asriel Dreemurr from the Undertale fandom.

Canon
Asriel's memories of Chara saved him and give us the Pacifist ending.

Both Chara and Asriel were best friends and before the events of the game decided to try and break the barrier of their world through a suicide plot. Asriel objected to the plan but was coerced into it by Chara. We don't know what Chara says, but Asriel responds with 'No! I'd never doubt you Chara' and 'I'm not crying. Big kids don't cry.'

Years later as Flowey, Asriel admits that Chara is the 'only one he really cares about anymore' and 'the only one who is fun to play with anymore'.

During the Genocide route, Asriel/Flowey admits if Chara is around he's okay with not destroying everything and might just be happy going up to the surface.

Fanon
Their relationship is ambiguous.

Although many fans interpret them as siblings, Asriel only refers to Chara as his 'best friend'.

Fandom
AO3

AO3