The protagonist, Ikuto Momosaki, is an unpopular and introverted 16-year-old second-year high school student.

On the afternoon of the day his mid-term exams ended, he spots a popular, outgoing couple wearing the same uniform. Naturally, he feels envious, but he is speechless when he sees the girl's face.

The girl was someone Ikuto knew very well — Ren Momosaki, who had become his sister due to his parent's remarriage. In other words, she was his stepsister.

As her brother, Ikuto grew concerned about the boy next to her and immediately tried to investigate him… but unsettling rumors surrounded the student.

Worried about his stepsister, Ikuto subtly asks her about her boyfriend. However, his stepsister becomes enraged at her overprotective brother's attitude — and Ikuto, filled with anxiety, consults his socially awkward friends. For some reason, he is advised to "steal her away"…

This has also been posted on Kakuyomu.