One day, Shimizu Seiya wakes up in a hospital bed, from his little sisters he learns that he was carried there by an ambulance. As he has no memory of what happened, he asks his little sisters about it, and they answer...
"Onii-chan, you had a technobreak..."
A technobreak, in other words his heart malfunctioned because of a too long masturbation period, he lost consciousness and was found by his little sisters which saved his life. But the day before he was supposed to be just doing university assignments and he had no memory or intention to masturbate...!
Apparently the reason for this was the high amount of energy drinks he drank in order to work overnight. The drink was studied in a laboratory and found to have included substances forbidden by law, and currently was being recovered by police. The drink caused Seiya to become extremely aroused and was unable to to stop masturbating, he continued that overnight until losing consciousness. Apparently the symptoms would eventually disappear and his body will go back to normal. Meanwhile Seiya felt relieved, his little sister gave him a certain item.
"It's a chastity belt, Onii-chan."
While embarrassed, his little sister continued.
"At this rate you won't be able to stop to stop masturbating, so..."
"We have decided that we will manage your ejaculation!"
These words astounded Seiya and so, his days of having his ejaculation controlled by his cute little sisters began.