So, you may have noticed in other covers that Serin has a rosary wrapped around his hair and resting over his face. Long story short, he's got a piece of a god in his eye socket and while this god isn't evil, it puts out a lot of power to the point where the pieces are attracted to each other and something bad(?) might happen if the pieces come back together. The rosary keeps the power locked away.
Serin is a cinnamon roll, so of course if he took hold of the power of a god, it might make him a little less... amicable? Well, what's a little blazing fire and absolute rule between friends, right? Ha ha ha, it's fine, it's just a cover after all....
BTW, if this outfit is giving you deja vu: Trinity Blood.