Cerberus

Season 1, Episode 10: The Omen

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Hiiro learns the magic spell of the Kokuu blade, a weapon which will strike an enemy from afar. Hiiro is far too terrible a swordsman to put it to use, but Master Theo notices that he has incredible power. Theo realizes that not only is Hiiro keeping Dagan Zot's heart in check, Dagan Zot is the only thing keeping Hiiro's heart from going out of control...