Mahiro, who was fed up with her boring daily life, one day encounters a groper on the train. A man who had been harboring lewd fantasies about Mahiro happens to witness this and his restraints of desire loosen. Then, on a hot day, the two end up on the same train again. The man, driven mad by the smell of her sweaty armpits, starts molesting Mahiro, but things don't stop there...!
