INFO:

The man has a monotonous job punching tickets for the Japanese railway.
One night, while walking home, he saves Jun from getting raped by two
hoodlums. A few days later, he sneaks into her house but gets
discovered. Later, as he watches his son subdue an insect with a
chemical, the man gets an idea to subdue women while they’re sleeping so
he won’t be discovered sneaking into their home. His new hobby spirals
out of control as his confidence grows.