My Stepmom's Daughter Is My Ex: Volume 5 by Kyosuke Kamishiro

G-Greetings. For those unaware, I am Isana Higashira, Mizuto-kun’s best friend, aka the girl whose advances he most recently spurned. There’s clearly been a development in his relationship with his stepsister, Yume-san, during their family trip, but it’s of no concern to me. After all, I simply wish to continue being his friend.

Strangely enough, others have been assuming that my own relationship with Mizuto-kun has evolved, in a sense. Some, in fact, are under the assumption that we’ve become romantic partners! Very curious indeed. However, I’m content with our current relationship, and I’m positive that he is as well. No matter what pressure we find ourselves under or what salacious situations we wind up in, we will always remain the best of friends, and I wouldn’t want it any other way. Of that, I am...certain.