きみの横顔を見ていた [Kimi no Yokogao wo Miteita] Series by Rumi Ichinohe

One might call Hikari extraordinarily ordinary. One day, she takes up a new hobby-imagining what a romance would be like between her pretty friend Mari and the cute guy in their class, Ohtani. It's all in harmless fun, until the roles start to get tangled in Hikari's mind. Does she really have to be just the best friend in this love story? And just who is on Ohtani's mind when his eyes drift away…?

Ohtani is a funny, nice guy. When he saw Mari smile, he couldn't help but fall head over heels. She is a quiet and shy girl, but thanks to Hikari and Asagiri, Ohtani has been slowly getting to know her. But her eyes seem to drift away in the direction of a certain teacher…