How do you unlock that subplot? I didn't bother completing all sub-stories on my first go since I wanted to play through the game again with items rewarded from the Climax Battles.
On another note, I have to say that Kiwami was surprisingly disappointing storywise compared to Yakuza 0. Plot points were incredibly rushed with characters you barely got to know or understand. If I didn't play Y0, Nishikiyama's entire character arc in this game would have been completely irrelevant to me without playing Y0. Also, introducing an obnoxiously evil villain at the end with little to no character build up was hilariously bad. I also wish Yakuza 0 actually had an arc with Nishiki's sister so we could at least feel some sympathy and connection to his plight. Nishiki's also barely in the game. I was expecting him to be a very involved villain, but you hear more about him in passing rather than experience his villainy.
When it comes to the actual sub stories and experience, these were not as good as Yakuza 0. I have to admit that though I disliked money being tied to experience and abilities in Y0 at first, it definitely grew on me because it not only fit story wise; it made money and side activities useful in general. Money in Y1 is almost pointless. there's really not much to spend it on other than trying to get achievements. Also, allowing the Dragon of Dojima skill tree to level up infinitely gave use for the access cash you built up. In Y1, once you max out the skill trees, there's nothing to do with the experience you gain.
Kiwami is still a very enjoyable game overall, but I was honestly underwhelmed by it after leaving the euphoric high that was Y0.