Chasriel

Chasriel is the non-binary ship 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 one sided suicide pact where Chara agreed to die so the two could merge and become more powerful. Asriel objected to the plan but was coerced into it by Chara. The player doesn'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 No Mercy route, Asriel/Flowey says if Chara is around he's okay with not destroying everything and might just be happy going up to the surface.

The two both have matching lockets inscribed 'Best Friends Forever' and their relationship is highly codependent with lots of strong feelings. Asriel, in particular, says that he has a hard time going on in a 'world without love... a world without you' (referring to Chara).

Asriel's relationship with Frisk is also heavily influenced by the fact Frisk and Chara look similar.

Fanon
Their relationship is ambiguous.

Asriel only refers to Chara as his 'best friend' but many also interpret them as siblings due to the Dreemurrs watching over Chara during their time underground.

The ship has struggled to settle on a specific tag throughout its history, with 'chasriel', 'chariel' and 'charasriel' all being about as equally common.

Fandom
AO3

DeviantArt
 * chasriel tag on DeviantArt
 * chariel tag on DeviantArt
 * charaxasriel tag on DeviantArt
 * asrielxchara tag on DeviantArt
 * Asriel-X-Chara fanclub on DeviantArt