Hey, thanks for the ask ☺️
7. The obvious answer would be his armband, which he canonically sleeps in, but that's too boring an answer, so I'll say his bright red fundoshi (which Nuri pitched as Ryuu's DLC outfit because he was running low on time to design something lol). They're his lucky undies :D
12. It's not that crazy, but I once pitched a phantom thief x detective AU to a friend with Barok as the detective and Ryuu as the thief. Sherlock and Iris are Ryuu's "guys in the chair" who develop his gadgets and guide him when he breaks into places. Ryuu is, of course, a Robin Hood type thief, who steals to help people, and his inspiration is Klint, a phantom thief who helped him out of a tight spot in his childhood. Barok has no idea his bro used to be a legendary phantom thief! Anyway, I didn't plan out too many other details besides those, but I still think about it sometimes.
13. I've collected a few BarokxSherlock doujins and they can be awfully fun sometimes. I haven't had the itch to draw much recently so idk if I'd ever do any fan art of them, but the bitchy exes vibes compels me.