My take on Yukishima and how their relationship evolves the more they get to know each other,
At first I think they would me like a weird friends with benefits kinda relationship and keep their relationship a secret beacose neither want to put a label on what they got going on and how yukio Don't want to "dirty" he image beacose of renzou's entire reputation
But after a while they get to know each other and it turn into a real relationship as they find comfort in each other pain and happiness alike, their what you could consider toxic beacose they both are heavily mentally unstable and yet they keep each other in that state and find comfort in it, which get worse during the illuminati arc, but despite that they still love each other unconditional not that either of them would admit it
And after the war they relationship shift to something more healthy despite them still feeling comfort in their pain, they unintentionally get a but better by being here for each other and and being the only one that understand each other the way they do, two teen/young adult that are more fucked up in the head then they'd like to admit, it's also at that time where the rest of the exwire notice something going on but don't say anything
After some trail and error they finally get to the point where they have a healthy relationship (to their standards) and know each other like the back of their hands,
It's exactly when they reveal their relationship in their own way, which is like that:
* renzou his head on yukio's lap as he absently trace the scar on his forehead while reading and renzou watched something on his phone he now and then showed to yukio*
*the rest of the exwire stare confused and speatchless by the display of affection*
Rin: Huh...what is going on?
A confused renzou and yukio staring at him: uh?
Izumo: What do you two have going on??
Renzou: oh that right we didn't tell you were dating!
The exwire expect for renzou and yukio: What!?
(That was a long ass rent god damn)
