Post-canon Yin Yu being the only one Hua Cheng trusts to look after Xie Lian if he's not around (besides Yushi Huang, but she's generally unavailable.)

(Xie Lian does not need looking after. Irrelevant.)

It becomes this strangely intimate though platonic dynamic where Yin Yu is the only other person allowed in their bedroom; the only person allowed to see Xie Lian fluffy and half-asleep and debauched. And when some disaster makes Hua Cheng slip from the bed in the wee hours to go crush problems with an extra layer of irritation brought on by having to leave a cozy bed full of post-coital snuggles, it's Yin Yu who brings Xie Lian breakfast in bed. And Xie Lian would hate it to be anyone else; Mu Qing and Feng Xin would shriek and fuss over his love-bites and the way he winces a little when he moves, and anyone else would awkwardly avert their gaze and fluster and stutter. But Yin Yu is just like, "Would His Highness like a Tylenol with his orange juice?" and Xie Lian kind of loves him for that.