Now, how do you turn Yagami's already really cool sidekick into one of my favorite video game protags?
Give him an absolutely amazing storyline that gives Kaito some much-needed additional depth and backstory and a splendid cast of supportive characters and antagonists that all have great chemistry with Kaito; with Jun, Mikiko, Kenmochi, and Kyoya being the highlights, and the first two particularly being some of my RGGverse favorites, as Jun is one of the very few well-written kid characters and Mikiko is one of the very very few well-written women in the RGG series who actually has some agency, actually does something, has a personality, can kick ass, and is relevant and active in the story at hand instead of barely doing anything (Saeko and Seonhee in Yakuza 7 lmao) and is an absolute baddie to boot, and you got yourself a real winner amongst the RGG Studios pantheon.

The only caveats here are the DLC's lack of side-content like sidecases, the fact that Kaito gets a recycled Brawler and Beast, which is pretty much just a pretty basic and janky moveset port with very minimal additions to make it stand out (hopefully that gets fixed in the sequels by giving him a new moveset which by god he deserves) but again the fantastic story more than makes up for it, Higashi getting shafted AGAIN, and Mikiko and Kyoya not getting enough screentime, with a lot of it being show-don't-tell, but I'm willing to give RGG the benefit of the doubt, as this was their first character DLC (no, Majima saga does NOT count) which was pretty short, running at 6 hours, but hey, the lack of Mikiko screentime will most definitely 100% be fixed in future sequels, which I am very hyped to see. And let's not forget its pretty overexaggerated 30$ pricetag, which is still pretty fair when compared to Gaiden's absolutely ridiculous 50$ pricetag lol

Overall, please do check this one out when you're done with the base game if you haven't already; it is so worth it.