Daidouji Senpai is the last playable character you get to used in Senran Kagura: Shoujotachi no Shinei. She can only be unlocked after defeating her in the additional key mission in found after completing the game. Warning, she’s extremely strong and all characters will be forced to fight her 1-on-1 so 5 consecutive battles in total.
I had problems defeating her at first, took me around 6-8 attempts because losing just one battle and the whole mission will start all over again.
Here’s how she looks in game.
…Doesn’t she looks like Tsunade from Naruto?
And she can’t change costumes, only alternative color and accessories.