I still haven't finished the whole thing as the english translation is still coming out but there's only one thing that disturbs me in the manga and this is not the age gap itself but the fact that he basically watched her grow, literally raised her and ended up like that. There's a sensitive line when it comes to stories with age gaps, especially when there's a minor included and I think if Keiya has waited a bit more until Isaku turned 18 would have been better, at least for me. I think both in Europe and Japan the age of consent is between 14-18, in Japan I'm pretty sure it's 14 which explains almost every manga available out there. I do not like that, but it is how it is. The fact that she likes him, though, makes it way easier for me. I've seen students in school who had relationships at 15 with way older guys so that's not even something new to me. As long as the girl likes the guy and the relationship is safe for both I got no problem with it, which probably keeps me hooked to this manga. I took some time to get over the "he raised her as a little sister" moment though in order to continue.
I love yakuza stories, I like the affection between those two so I'm patiently waiting for the rest of the release to see how this whole thing ends.