"Fault!! Service: Aratanaru Rival" is a steamy hentai OVA based on the erotic visual novel by Ciel, following Shuuichi as he navigates his second school term amid relentless romantic and sexual advances from his girlfriend Ai and sister Mio. Tensions escalate when the tennis club leader Reiko pushes for a cosplay café at the school festival and runs for student council, only for a mysterious transfer student to shake up his already chaotic harem dynamics.