The Kōga Must Die is the third episode of Basilisk ~Ōka Ninpō Chō~.
A dark force descends upon the Five Treasures as they are attacked by a mysterious ninja... or is he a ninja at all?
In the early days of training, the young ninja practice, but are reminded by Gorone Negoro that they do not fight for Kouga nor Iga, but for their leaders. They also learn about the powers of Hibiki and Hachirou. Back at the Ooi River Gei'in and Kaso rush out looking for Kazuma and find him bound to a water wheel and killed by his own Heaven's Lyre. The meet the killer, but when Kaso attacks her, his own Grass Fire flames consume him. She reveals her name is Kujaku Tsuibamu, one of the Joujinshuu, enemies of both the Five Treasures of Kouga and Five Flowers of Iga who are fated to die that night. As he talks Gei'in sends his poisonous Firefly Squid below Kujaku Tsuibamu, but she avoids it, and even when he sends a burst of poison towards her, it returns to his body, killing him. Hachirou detects that four Treasures of Kouga are dead and returns with Hibiki to the village. Gorone reminds them that they must put their clan differences aside, and sends Rui and Shichigen to warn the Five Flowers of Iga while the others stand guard. Back at the Ooi River Tadanaga is confronted by Joujin, a former palace official who tells him that he will be executed by his brother, Shogun Iemitsu.