True as it may be Yuu would run the risk of being put in danger with being with certain twst boys...the ones that would be the most in danger are the peeps trying to hurt their partner or friend.

....and some of the boys are less forgiving than others.

....and some of the boys are less forgiving than others.

(referencing this shrimp annon post)

The two who immediately come to mind for me when I saw this ask were Vil and Malleus. I know I said that being with Vil wouldn't be as much of a danger and I stand by that but... look he is stupid intense and very haughty when he feels vindicated about something, if someone threatened his partner they'd get stomped to death and wouldn't even have time to enjoy it.

Malleus is a tricky one since we don't exactly know how the government of his kingdom functions, but we do know a bit about how his powers do and he's damn near unstoppable. If something happened to Yuu it wouldn't be pretty for the people plotting against him. If he wasn't being threatened with something that hit a bit too close to his childhood traumas he might find the whole thing amusing. But he can't, not with how real the threat of losing you could be. He is going to take this most seriously.