Hmmh I'm bad with headcanons I always start to talk too long...well, appearance-wise, I like what ONE showed us. Slim and unevenly cut hair.

I like the idea that he stays shorter than everyone else. He's still short and soft-looking but has muscle underneath, not to the extent of his old club but so that he feels proud of himself. He sometimes manages to drag Reigen out of bed for morning jogs around the neigborhood. Not a high success rate.

He's also more popular! He's been since his teens, and Reigen says the world is just realizing how handsome he is, as much as that flusters Mob. He turns down the occasional confession and then excitedly tells Reigen about them. Reigen's just happy for him.

Despite having his own apartment he still kept coming over to Reigen's tiny place instead. They get engaged, not suspiciously soon, around Mob's 23rd. Reigen was burning the ring in his pocket since Mob was 16, so it didn't fit when he proposed, and Mob cheated a little with his powers because he couldn't wait to have it on.

He's struggling with work – Getting used to the hell of actual worklife is much tougher than it was at the S&S office, and Reigen does his best to not let him burn out too young (be it a massage and a cozy night or marathon fucking). Reigen tries to close the office around the same time Mob gets off work so they can go for ramen like old times.

They'd want to work together at S&S again, but that's hard to do so that they could afford renting in their apartment. They could do it once they've saved up enough to buy their own place.