Maison Ikkoku Episode 69: Underwater Battle! A Suspicious Hickey on Godai!
Episode 69 of 96 of Maison Ikkoku, aired August 5, 1987, 25 minutes. Available with English subtitles and dub where released.
Episode summary
When the gang goes to a hotel resort, Godai must explain to everyone (including Kyoko) how he got a mysterious kiss mark on his shoulder.