Summer Love Begins with a Lie

Kaoru ran away from home and is found drenched in the rain by her homeroom teacher, Mirei. At school, Mirei seems like a responsible adult. At home, however, she gets drunk in the middle of the day while chattering away. But she tries to help Kaoru come to grips with her troubles... It's the beginning of an unsteady romance between two people who haven't quite grown up yet.

(Source: Ichijinsha, translated)