Rather than jealous, I think Yashiro was angry at seeing the tattoo because Yashiro had tried so hard (before time skip) to keep Doumeki from ever really going down the path to becoming a yakuza member. To get your tattoos means there's no going back for you, you're yakuza in the eyes of the world. Unfortunately, Yashiro gave up any right to control Doumeki's path when he abandoned him, and Doumeki made the choice to become yakuza in the hope that it would help him cross paths with Yashiro again eventually.
Ooh that's so interesting and gives this an even deeper meaning
(▰˘◡˘▰)
Man they break my heart both of em , I want a happy ending
Ugh I kept thinking about Doumeki's tattoo. Surely that made Yashiro jealous because it's like he promised his life to the yakuza and not him. And then those rumors of the madam. Man he just couldn't *really* get into the sex thinking of all that. But I mean, you started this asshole! You brought him into this business and you pushed him away. Don't be getting all jealous now!
But it is interesting and kinda cute seeing Yashiro jealous. Maybe he'll finally admit to his real feelings.