Huaxin has been on my brain for a minute and it's a travesty how much there is a lack of HuaXin/HuaFeng content, so here’s a bunch of silly headcanons to fill up that void lol
(There might be hints of HuaFengLian but it’s primarily focused on the two)
A lot of their bonding time consists of dueling/wrestling with e/o. It's how initially they were drawn towards e/o trying to showcase their strength and take the other down and now it kinda serves as foreplay for the two (HC loves taking advantage of it, FX is... less aware)
HC: idk I just don't think you can pin me down
FX: Oh yeah?! Well I'll just show you— *takes off his shirt*
HC: ¬‿¬
Hua Cheng originally was appalled by Feng Xin's taste in humor but over time he learned to weaponize it to see Feng Xin lose it and snort in laughter. The best reaction he got was when one time he got Feng Xin to crack during a Heavenly meeting and FX was crying as he was holding back is laughter but failing.
Feng Xin creates up silly names for some of Hua Cheng's disguises that he teases him for, but some of the names end up sticking and it's a helpful identifier when FX is trying to find him somewhere and knows what disguise it is by the name, or when HC needs a random identity
FX, in their private communication array: Okay I'm at the market but I don't see you yet
HC: I told you I'm wearing a yellow outer robe and carrying an umbrella
FX: That doesn't narrow anything down
HC: ...
HC: I'm Xiao Long (little dragon)
FX: Oh okay that helps
Feng Xin likes playing with Hua Cheng’s hair. The inky color always catches his eye, the length of it amazes him and all the ways HC can style such length, and the softness of it soothes him. The only problem is that FX can’t do much with hair besides a simple braid— anything else he tangles it up— so he has to stick with occasionally braiding it or asking to comb it to have his fill
On the flip side Hua Cheng can do anything with Feng Xin’s hair with ease. He's allowed to do whatever but he likes putting up FX's hair in it's usual style and he also goes out of his way to make sure it gets moisturized b/c FX is not when to often put effort in caring for it other than a simple brushing.
They wear subtle hints of their relationship via accessories. For Feng Xin it's earrings or rings Hua Cheng has gifted him or a jinbu that's styled to whatever outfit he's wearing. Hua Cheng tends to wear colors that represent FX via ribbons in his hair or on his belt. He has a special charm Feng Xin hand-crafted for him that he near wears constantly to show off what his lover made him and that he has the protection of Nan Yang to other ghosts.
Feng Xin is very cautious of touching E-Ming, not b/c he's afraid of getting hurt, but b/c one day FX wanted to be courteous and polish up his lover's special spiritual sword and when he does any type of maintenance or polishing for a weapon he's very thorough... the chain reaction of that incident left him limping for a week
Feng Xin casually said one day that none of his temple statues looked like him and Hua Cheng thought he was bluffing, but after looking through every. single. statue. he realized FX wasn't and had a crisis about it
HC: I don't understand how none of them don't even look like him! You would think that with all the prayers he gets about Ju Yang they would also know his basic facial features!
XL: It is very surprising
HC: Someone has to do something about it, it's simply an embarrassment for him to have
XL: Yes, someone could...
HC, in denial: He should get his deputies to take care of it, but knowing them they'd get a subpar craftsman to take care of it—
HC later, halfway through sculpting one statue with another stone block already in the works: ...Goddamnit
Hua Cheng usually calls Feng Xin gongzi in bed, but his favorite when he's really domming is didi (I'm a bottom FX fan alright)
In reverse however, Feng Xin calls him didi
It shuts Hua Cheng's brain down when Feng Xin places his hand on his lower back and guides him around. The warmth from his hand is all HC can focus on in the moment
In reverse it dumbfounds Feng Xin when HC holds his hand. Those elegant hands can be doing something else, holding someone else, but here they are caressing his knuckles. They're both whipped your honor
Somehow they created a roleplay scenario they love doing where Feng Xin disguises himself and acts like a righteous young lord causing a fuss at the gambling den and HC swagers up to "take care of him". The ghost denizens know what they're doing and they are many emotions about it
If they were together during the events of canon they're both actively screaming at each other in their communication array about the decisions they're doing with XL and panicking
That's all I got for now but may post more in the future cause I feel they're a fun dynamic/ship to explore. Feel free to share some of your own :)