秘めゴト 新章 ～若妻絶頂性教育～

The protagonist, Sanjou Tsunsuke, is an ordinary student attending an ordinary school.
His athletic ability, grades, and looks are all average, and he seemed to be living an ordinary life. But one day, all that changed when his young stepmother showed up.
His father, a folklorist, had returned home from a field trip to a certain country, bringing home a woman as his fiancee.

Accustomed to his father's eccentric behavior, Tsunosuke quickly accepted that, but he couldn't hide his confusion when it came to his stepmother, Ami, who is almost the same age as him. The reason is... she is just his type. Tsunsuke's heart continues to be tickled by Ami's innocent personality, which, unaware of Tsunsuke's feelings, tries to get along with him because she's his stepmother.