Koibito Koukan Nikki

"Who should I love, my boyfriend or my best friend's boyfriend?"

Mana, a third-year high school student, is dating her classmate and honor student, Eira. One day, her beautiful and rich friend, Aimi, comes to her for advice, saying that she is troubled by her boyfriend Ren's cheating habit. To teach Ren a lesson, she suggests that they exchange boyfriends for just one day... But what is the true nature of her best friend, Aimi, that emerges from exchanging boyfriends?

(Source: Kodansha, translated)