New idol Arisa joins Seven Arts and is immediately forced to participate in the underground Obscene Sports Day. Ibuki, unaware of the true nature of the event, puts her body on the line to protect her junior Arisa. However, she ends up being overwhelmed and defeated in various lewd competitions. Meanwhile, Koharu (Kokoharu) mocks Ibuki while engaging with Kurozuka (Kurotsuka). Ibuki later discovers the shocking truth about Arisa, whom she desperately tried to protect.