Joke from the first Rei OVA. Keiichi had these curse swim trunks that were eventually forcibly removed by Irie, Ooishi, and Tomitake. After he found out why all the commotion to get them off, he jumped up claiming that there is still playing to be done, exposing himself to Rena, Rika, Mion, and Satoko. Mion made a embarrassed comment and Rena squealed about Keiichi's "fur seal" and finding it so cute.
Actually, in the actual VN form of Onikakushi, Keiichi shows Rena his "Mr. Fuzzy Seal keychain" behind the shrine to win the "make Rena have a 'kyuuute' overload contest". So I figure that it was taken from there, though I believe that scene was cut in the actual anime.
Yeah, the scene was cut from the anime, and can be find only in the VN, in Onikakushi part. But Keichii was beaten, because everyone though the same thing than those guys, about an another "fur seal".
