Because I Don't Like My Big Brother At-All--!!

Season 1, Episode 9: Summer! Festivals! Brother and Sister's M:i:V

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Shūsuke goes to a Matsuri festival with Nao and Iroha, who compete with each other to try and seduce him. Meanwhile, the A.G.E Explorers go on a quest to find a legendary pornographic treasure and proceed to drag Shūsuke away to join them. However, the treasure they find contains zoophillic porn that proves too intense for them and they run away, with Shūsuke picking up Nao in tow. After watching the fireworks with Nao, Shūsuke goes to deliver some BL books to Mayuka, who once again becomes enthralled by his nipples.