This started in 1999, eh? That explains a bunch of things, including why there are so many manga out there that have taken inspiration from at least one thing from this series.
High Score Girl's followup, featuring Hidaka Koharu as a teacher, almost feels like the gamer reboot of this series honestly. I can't help but feel that the author of that read this work to get some inspiration. They're not identical, but they do "rhyme" in some of the developments.
So much so, that I can already tell what's going to happen in the future even though I'm only at chapter 50.
Edit: Ironically, I found out about this manga by looking up the artist after reading "Detective Doggy" (Detective Puppy really) on Mangamillion
https://mangamillion.shueisha.co.jp/en/title/370
That one being about cops rather than the Yakuza. I'm glad I did. I don't think this series would ever get translated for profit given its age, niche content, art style, and subject matter.