The protagonist is Yamazaki Shizuka, a worn-out salaryman working at a mid-sized company.

At one point in his life, he was the school hero—top of his class, excelling in sports.
But during his university entrance exams, he mixed up his answer sheets and failed spectacularly.
Around the same time, his father was laid off, leaving Shizuka unable to retake the exams. He ended up at a safety-net university on a scholarship.
His college years were far from what he’d hoped for, and he grew cynical. Job hunting went poorly, and the company he finally landed a job at let him go without a second thought. Since then, it’s been a cycle of job-hopping.

His only solace is attending concerts of a popular idol group.
Watching them shine on stage, he often mutters to himself,
“Alright, starting next week, I’ll get serious, divorce my wife, and marry one of them.”

One day, during his commute, he spots a high school girl studying English on the train.
“I used to memorize vocabulary like that on the train too,” he thinks, feeling nostalgic.
As he gets closer, he catches the sweet, unmistakable scent of a high school girl…
Taking advantage of the train’s sway, he casually brushes against her lower body.
Whether she doesn’t notice or is too focused on her studies, she doesn’t react.

“Huh, maybe it’s okay to touch her after all.”
And with that, the protagonist’s descent begins.

“Listen, associating words with sensations helps you remember them better. You’ll memorize even the toughest vocabulary if I touch you like this.”

Thus begins the protagonist’s perverted “English lesson”!

[Translated from dlsite]