2 thoughts:

1) I totally agree that more unique ninja should be added, since there really are dozens (maybe hundreds) of them in the franchise that aren't here yet--most of them kinda terrible in combat, but a welcome and fun addition all the same (and a Naruto game that's labelled OFFICIAL should have access to every Naruto character that's ever been in any licensed media--game, manga, movies, etc)--and besides, by only adding stronger and stronger ninja from the series and you eventually hit a wall: a ninja with 2 million base initiaitive, an immunity to debuffs and to immunity suppression with a 0 chakra mystery that's a guaranteed hit and has no battlefield cooldown that kills every ninja in the field without the possibility of reviving.

But I get that Oasis isn't the only company involved. A lot of what you do is translate existing content to suit the language and playing styles of western countries.
So, I was wondering, if we have a suggestion that goes beyond what Oasis can implement, like replacing core game mechanics or changing its engine, to whom and how would we make that suggestion?

2) I like the idea of additional versions, but having them being separate ninja seems incredibly tedious, and somewhat confusing in the long run. Right now, if you have 100+ ninja, scrolling through all the different versions can be a headache. However, conversely, the ninja upgrade system is also so basic that it's often very ungratifying when a ninja's stars go up, only to offer a 5% stat increase. So I propose this: merge the two.

You've already done this with several characters--giving them a different appearance and changing a skill slightly after an upgrade (eg, gaara, kushina, naruto, kimimaru). I think it should be taken further though. With a few rare exceptions, the story in the anime/manga has a very linear progression, as does its character development, so I think you can safely have a different star represent a very different version (when applicable for that character). For example, 3 star Sasuke could be susano'o, 4 star could be the one from the end of the series, 5 star could be the one from Boruto

("yeah, but I spent months pulling in the treasure to get susano'o Sasuke, how's that fair that others get him free"). I hate to say it, but the reality is, with any substantial change comes substantial sacrifice. Before a new building is constructed, what was there before must be cleared away. Perhaps the upgrade system can be changed to have more stars, or get them by some way other than ninja fragments?

Further, in the Transform section, you already implemented the ability to transform the main's appearance to reflect a lower-star version of a ninja. So, I imagine, if there are those that prefer using a earlier version of a ninja in their lineup, that that same feature could be slightly modified to work here too.