Seimi's father-in-law, Sōtarō, was a teacher at the couple's alma mater and had also been Seimi's homeroom teacher. After Sōtarō retired, he got drunk at his farewell party on unfamiliar alcohol and fell down the stairs, breaking a bone. As Seimi diligently took care of him, it didn't take long for Sōtarō to become aroused by her.
