16-sai, Sensei ni Yogoreteku

Synopsis

"Can we keep it a secret, just between the two of us?'' In an empty classroom, the teacher kisses me… Ena, a serious but shy high school girl who is overshadowed by her popular and talented older sister, secretly confesses to her art teacher, Asami. She is in love with him, because he was kind to her and treated her as a unique individual, not just someone's "younger sister." Ena couldn't tell anyone about her feelings, but she did tweet about them on SNS. But one day, she witnesses her beloved Asami-sensei and her sister kissing! Ena could only cry in anguish, as her love begins to become something worse!? (Source: MechaComic, translated)