Itsuki Ichigohara is a married high-school teacher in her late 20's, who finds herself involved with a high school girl, her student, who is 10 years younger. The student's name is Rin Togawa. She is taller than Itsuki, with a beautiful face, mild-mannered but a little childish. She is a good girl, but she has had problems in her family life, and as Itsuki tried to counsel her, they somehow ended up kissing each other in bed. This is definitely an adulterous betrayal, not to mention a crime. How could she have got herself into so much trouble that could only lead to her own destruction?

— How could I have let this happen?

It is a lewd and immoral, but somehow warm relationship. A love story between a female teacher and her female student.

(Source: Kadokawa, translated)