Sasaki to Miyano: Koi ni Kizuku Mae no Chotto Shita Hanashi.
Plot Summary: It's November. A student who has lost his keychain comes to Miyano and his friends, who have taken over the disciplinary committee's workload. On a whim, Hanzawa proposes the establishment of the "First Lost and Found Detective Agency," which goes out on a search party.
Other name: Sasaki to Miyano OVA, Sasaki and Miyano: A Little Story Before I Realized Love; 佐々木と宮野 恋に気づく前の