Characters swap round ever 4 chapters, and I think? you get point of no return prompts before the climatic battles (at least you do before the end of the game). You can either do everything in one run or just hit stuff up in premium adventure mode. You will gain the ability to switch between the guys at the end of the game and also share all your items so if you want you can leave stuff to later if you'd like. Keep in mind though:Oh when Kiryu hops on the bike and starts riding it?
BTW in 5 how often do you switch characters? Should I worry about doing everything with Kiryu right now or progress first to get a taste of everyone.
Haruka doesn't get a shared item box, at least in story mode. I'm also unsure if your supposed to do all her stuff before the end of the story or can do it later in premium adventure mode (to be on the safe side I wrap everything up before the story ends with her)
Also, due to item box sharing - DO NOT pick up locker keys as Haruka, as that means you can't share the items obtained from said lockers with the guys. And since there are lots of modding items and Casino cheat items to be had, you really want to leave that stuff to Akiyama.
Lastly, I tended to stop doing side stuff after I hit the level cap (20) for each of the guys. This is because you limit break in the final chapter if you meat a certain trainer, then I loop back and do the rest of the content to get the EXP (its just easier to hit max level this way rather than wasting the XP, especially if your planning on doing the arena you'll want to be as close to max level there as possible)
Also, completely forgot that Haruka also has a missable trophy. At one point you get an option to keep on going or to give up. DO NOT GIVE UP! If you do it locks away one song in Karaoke, which again makes the 100% completion list impossible to clear.Thanks for the heads up! Thankfully I didn't sell anything, I just put everything in my item box.