Touch me, please

 Every morning, Matsui finds it sexually satisfying to get molested in the train. One day, a good-looking underclassman, Aizaki, happens to see him getting molested...Aizaki asks him, "can I molest you tomorrow onward?" 

Since that day, Aizaki's intense molesting begun with Aizaki verbally abusing him, using sex toys, and teasing. 

"What are you doing making a mess in a train, Senpai?"

What is going to happen to Matsui with Aizaki's molesting play that gets harder and harder everyday?