Mitsuki, who was my classmate in school, was the person of my first love. I was attracted to her, seeming pure and quiet, but I never got to confess my feelings. When I heard she would attend our class reunion, my heart raced—but then, from her, now sophisticated and mature, came a shocking statement: "Next time, I'll reach 100 partners." That pure girl had lost her virginity and become a serial dater! Worse, right in front of me, she started having unprotected sex with my best male friend... I was forced to witness this and felt a surge of anger...