Xingyun

Xingyun is the slash ship between Xingqiu and Chongyun from the Genshin Impact fandom.

Canon
In Chongyun's Voice-Over lines, he states that he admires Xingqiu for his devotion to chivalry and passion for reading, but has also seen Xingqiu's mean side. He is a common victim of Xingqiu's pranks and antics.

In his Story, it's stated that Xingqiu gave him the idea that, instead of attempting to reduce the effectiveness of his congenital positivity, he should search for an evil spirit that is immune to it. Xingqiu often gives him fake intel of sightings of evil spirits, and they come home empty-handed. Chongyun has no idea and blames it on his bad luck. Surprisingly, Xingqiu will try to lift his spirits after his pranks, doing things like getting him cold food.

In Xingqiu's Voice-Over lines, he states that he and Chongyun understand each other very well, implying they have been friends for a while. He also states that whenever you see Xiangling out and about searching for ingredients, she'll try to get you to try her newest recipe. He says that he'll usually get Chongyun to try it out.

In his Story, it's stated that Chongyun is the one who usually bears the brunt of his bizarre humor. Just like in Chongyun's story, it talks about how Xingqiu often pranks Chongyun by giving him fake intel, setting up traps in areas Chongyun practices in, etc.

In Xiangling's Voice-Over lines, she states that she always sees Xingqiu and Chongyun eating together at Wanmin Restaurant.

Fanon
The ship mainly sailed due to the popularity of the "Best Friends to Lovers" trope, and their dynamic. Many users enjoy their elemental chemistry; as Xingqiu is a Hydro(water) user and Chongyun is a Cryo (ice) user, both use elements that work very well with each other and are able to apply the "Frozen" debuff on enemies when working together.

Due to neither Xingqiu and Chongyun having any confirmed love interests, or very many interactions with other characters in general, Xingyun is a very popular ship for both characters.

Fandom
Chongyun/Xingqiu tag on AO3

Trivia

 * Xingqiu calls Chongyun "my dear".
 * Chongyun tries to form a "Victims of Xingqiu" alliance with the Traveler.