At Yūjin's high school home, his childhood friend Chihaya and his younger sister live together. While looking after his sister, Chihaya searches for his missing father. Yūjin secretly admired Chihaya, yet also saw him as a rival. One day, fed up with Yūjin's irresponsibility, his parents declared Chihaya would become his “supervisor”! Since then, Chihaya's bodyguard-like behaviour only increased Yūjin's irritation. Around this time, Yūjin was confessed to by an unfamiliar senior beauty. Floating on the air of having his first girlfriend, he boasted to Chihaya, who then declared, ‘Let's practise putting on a condom for when the time comes!’ When Yūjin refused, saying it was impossible, Chihaya offered to demonstrate right there and then...!? Features new illustrations.