Worst in the series. An obvious attempt to release a game quickly as RGG Studio's teams worked on superior projects on both the new and old engines.
Makes little attempt to work off of the plot threads introduced in the prequel, and as such, is a disappointing follow-up to Yakuza 0. Blatant reuse of moves and character models that gave me the impression of a corner-cutting development cycle.
The bosses have as little character as they did proper playtesting, in reference to their broken AI, heavy armor, and narrative disposability.
TL;DR
Start with 0 and skip to Kiwami 2, as Kiwami 2 more carefully addresses the narratives introduced in 0 in the way a story-based series of games should. Continue from there, because the series as whole is an accomplishment in longform storytelling and gameplay.