いつまでも息子のままじゃいられない！2 ～巨乳教師の母さんに家でも学園でも甘えたい！ ああっ、いいよ母さんっ！ はぁはぁ、すごく昂奮するっ！～

The protagonist, Ren, is an honor student, who is strictly educated by his mother and trying to succeed his father, who is a doctor.
He respects his mother a lot, but sometimes, he just wants her to be a little bit more lenient.

One day, he accidently sees his mother masturbating. After that, when studying with her, he keeps thinking of it and gets excited. Even though he is ready to be scolded, she calmly chided: "So this is why you can't concentrate." And promptly help him get off.