Oof, this one hits close. Because of his regenerative abilities his skin is immaculate, absolutely free of scars or blemishes and doesn't stay cut (or blown into chunks with how he shields people) for long, however there are three scars that will always remain. Their significance can't be fully explained, it's presumed they're death marks - the final wounds inflicted at the moment he died - but if that were the case for all souls then you'd see them on other characters too (especially poor Kazusa). The circumstances don't add up so it's possible they're something more than mere scars, hell, the formation they take in several instances look like the kanji for king and I am all for blaming Enma Daiou for everything wrong in his life. Either way, he hates them and he refuses to let other people see them. I used to be pretty secretive about it, couldn't say anything on the subject around pictures of him or just talk frankly on it because I felt he wouldn't want that - but it was like bottling it up. I got antsy not being able to talk about that side of him; it's important to who he is and to telling others how to treat him respectfully. I got upset with people because of stuff they couldn't have known because I wasn't clear about it, and at that point it really felt like my own fault.
The easiest way to deal with it is to talk really matter of factly about it and not think about feelings. If I bring him personally into it it still tears me up, because this is the shadow that looms over everything. It's not an elephant in the room so much as a great big rock crushing down on him in everything he does. It's something you don't learn til vol 5/7, and I guess for people who never make it that far it has no bearing on what they think of him, they don't see it, but I think it moulds everything about him from the start. You only have to look for it.
Oh and for an arc he had a dumb X mark on his back from a demon, it looked good but hurt like a bitch. Not worth it.