YukaIA

YukaIA is the femslash ship between Yuzuki Yukari and IA from the Vocaloid fandom.

Canon
Yukari and IA are both from the voice synthesizer Vocaloid, made to sing. Neither of them have any official personality or background and, essentially don't have any official relationship. They can be friends, enemies or lovers depending on the song.

Songs
The composer Nejishiki is known for using Yukari and doing romantic songs about her and IA. The song ICE BREAKER shows IA and Yukari having romantic and sexual relationships, while feeling guilty for it and hiding it from everyone, to the point that both wished to disappear. The song Piña Colada follows a similar topic, with IA and Yukari drinking and hooking up. The song Noble Rose is implied to talk about a guilty love, but now it is kinda ambiguous if it is a IA x Yukari song. The song Tsuki no Uragama talks about IA and Yukari wanting to see again a person from whom they separated. The song LAST DANCE talks about IA and Yukari wanting to make the most of one last night they have to have fun.

Fanon
YukaIA is a very popular ship within the fandom. It is likely that it started due the two being the most popular Vocalids that came out in the Vocaloid3 era. It doesn't have much competition, but it is sometimes rivalized against some rarepir such YuumIA or YukaMaki. The ship has inspired a few people to ship their respective counterparts, Akari and ONE.

The headcannons for the ship tend to variate. Some people view Yukari as the most cheerful of them while IA is more shy. Others view Yukari as a more stoic person while IA is more sweet.

In AO3, YukaIA has 40+ works. It is the most writted ship for both girls. In fanfiction, they often appear as a side relationship, thought they have many dedicated works too. There are also many songs and thousands of fanarts for them.