Oh lawd I just had my genius idea return to me.
Sakura Wars fighting game developed by Arc System Works. Or somebody else. Just make it amazing!
The char already all have different weapons (although a couple of them have a bit of overlap but who cares there's a lot of different weapons even still) so the potential is already there. Almost everyone has like at least one super move already, and the concept of a spirit gauge of sorts already exists in Sakura Wars.
Perhaps there's some interesting way to integrate the Koubu's. Make it so Koubu's only attack with normals. I have two ideas
-Make this thing where Koubu activation require 25/100 spirit meter activation cannot be cancelled until gauge runs out (or maybe it requires additional 25 meter). Take smaller percentage of damage, but at the same time have a certain kind of armor. Like, the idea of a focus attack for example, but it applies to all of your normals. Armor starts on activation, but only one point of armor so as not to be too overwhelming if you're fighting against someone with no Koubu. Maybe you get like limited number of Koubu activation per round, or something like Persona where its character dependent?
-What if it's like Tekken Tag, where there's two health gauges basically but if either one goes empties out, then you lose the round. But instead make the summoning of the mech risky or something, and while you're piloting it, it drains your spirit gauge. But that sounds kinda stupid.
And since most all of the characters are show performers too, perhaps there's a way to integrate that. Arc Sys seems to make a point not to reward turtling as it is anyway. All they have to do is not make the system not highly-momentum based by making the benefits of such things minimal. Certain things (like maybe taunting, high combos, dizzy, or maybe a dedicated command like Felicia's hyper charge thing) could yield more spirit.
It'll be so much different than Senran Kagura, and yet so easy to compare because of the obvious prevalence of women. And since fanservicey stuff is so saleable, maybe a lot of people will be tricked by the kawaii onna no hito's into buying the game (except if the anime series and Sakura Wars V are anything to go by, fanservice is more limited in this series. Except for maybe Erica and select other scenes I've seen, so nyeh)
And the people who already love Anime (ahem, Animaayyy) and waifus/ play FG's and like animay will be all over at least the concept (mostly women roster fighting). If advertised right, it should be able to attract those who otherwise wouldn't be interested.
Additionally, this concept of a Sakura Wars fighting game lends itself well to producing iterations within a series, as fighting game devs are wont to do. Start off with Tokyo edition (like 8-10 characters or something) and then Paris edition (main five) and then New York edition (Shinjiro, Ratchet, main five). Perfect! And by then there'll only be like 20 characters or a little over, so it won't be torture for matchups and learning new char like SFIV.
Sakura Wars is awesome when they play up the old-school action anime aspect of the series so it could be cool to see that in a fighting game. I didn't really hammer out these ideas and it's hard for me to understand how balanced or sensible some of these gameplay mechanics would be purely in theory but I think a rich system would make this more fun than something that's more fundamentals-heavy and stripped down. The idea of the Koubu's spiritual power that fluctuates, different weapon and theme color per character all lend themselves to a degree of creative interpretation that could produce something cool. besides the basic character concept should be fairly easily to convey (not much lore to worry about), the worry for the game is that there are so many fighting games (even accounting for the dead FGs)
ARC SYS SEGA WHOMEVER IF YOU'RE READING THIS START MAKING A SAKURA WARS FIGHTING GAME NOW PLS AND CREDIT ME. AND WHY HASN'T THIS BEEN MADE YET