I'm Sure I'll Love You Tomorrow, Too.

Mitsuki first met Imai Yoshinobu when her older sister Chizuka arranged for him to become Mitsuki’s tutor at home. Mitsuki was always slightly jealous of how Imai-san and Chizuka were classmates in college and always had a good time together. It seemed that Mitsuki would never even have a chance with Imai-san as long as the grown up and beautiful Chizuka was there. One day, Chizuka broke up with her boyfriend, and Mitsuki, afraid that Imai-san would now pursue Chizuka, told Imai-san that Chizuka already had a new boyfriend and that he should pick Mitsuki instead. Surprisingly, he agreed, but ever since then, Mitsuki’s conscience has bothered her… Can she hold on to this happiness that she achieved through a lie? Volume 4: The After School Lair, G-Line Romance