[@Sir Lurksalot]
Maybe Kurokono's grandma happened to be the daughter of a Yakuza head and both of them would compete for the affections of the woman, and would eventually invite trouble from the Yakuza. Haven't fleshed out that much on that part of Ryuunosuke's life, so you call the shots :3 . But Kurokono's grandma would die before he was born ~~

Edit: Perhaps his grandma died at the same day Kurokono is born, that would sound fun haha :X ~