Game's pretty great, love the animations. Though probably gonna wait a long time before trying it again, I lost a bunch of progress cause of the Tsunade fight lol. Even with max stats didn't seem winnable and I died, wasn't expecting it. XD I prefer having just "retry" options in these kinda games it's easy to lose track of making saves.
Yeah, she's kinda a boss (in RPG standards), thus OP, so you needa prepare & think.
Some tips, if you fight her:
1. She can heal herself, and does revive once. So you gotta 0 HP her twice.
2. As she's OP, debuffs are your friend; aka poison and stun-lock her.
3. You're gonna need to load up on pots, as she's a boss.
Otherwise, get all girls, and, as someone else in the thread pointed out, it does mean all, even the sides to 'max' level (aka girls at like 5, while the sides at 3-ish).
PS. Time rewind ninjutsu for you! -- Renpy has both a rollback and autosave feature, so not all hope is lost! In the Save/Load screen, there should be an Auto selection, so you can load that, though it's kinda funky, so some progress may still be lost. Or, if you have a save from the battle, load that and scroll back to sort of redo some choices!