Senran Kagura: Ninja Flash

Season 1, Episode 4: Seaside Training - Shinobi Island

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Kiriya takes the girls to Shinobi Island to train. Two more dark shinobis, Mirai and Hikage, attack. As with the other battles, neither Mirai nor Hikage took their battles seriously and left rather abruptly. However, Mirai revealed to Hibari that she is a freshman at the Serpent Academy for Girls, leading Kiriya to inform his students that these dark shinobis are also from that same academy.