Ryouko Yanagi operates a coffee shop near protagonist Arahama Yuu's residence in the OVA adaptation. She possesses brown hair styled short with a curtained middle part, violet eyes, and a mole. Her figure features notably large breasts and hips. She typically wears a turtleneck sweater, pinafore dress, boots, a necklace, and occasionally torn pantyhose.

Slightly older than Arahama, Ryouko adopts an older-sister role. Their intimacy developed after he frequented her cafe for extended periods. Though aware Arahama primarily views her as a sex friend, Ryouko secretly harbors romantic feelings for him. Her sexual preferences include breast sucking, paizuri, and creampies. She expresses a desire to bear his child, believing impregnation would allow her to provide him with daily milk.

When confronted alongside Arahama's other partners by Shimizu Misako—who demands he end casual relations and choose a spouse—Ryouko is among the five women who reveal their wish to marry him after he rejects committing to any single one. Her participation stems from this unacknowledged deeper attachment.