Mama wa Doukyuusei

Kisaragi Ryou's life is marked by loneliness, having lost his mother at a young age and often left to his own devices with his father away from home most of the time. His solitude is disrupted one morning when he discovers a naked woman in his house, prompting him to leave for school without fully processing the situation. Later that evening, his father returns home and introduces the woman as his intended bride, revealing that she is none other than Ryou's classmate.