Saeki Nozomi is a nurse working at the hospital where her cousin is staying due to an illness. At this point in the story, she is married but alone while her husband is on a business trip. She is also feeling a bit horny as her period is approaching, but she tries to remain faithful to her husband and only flirts with her cousin, whom she considers her little brother. Yumi is the guy's sister, who also works at the hospital as a trainee since she is studying to become a nurse as well. She has strong feelings for her brother and worries about him a lot, but she doesn't cross that line...