Saiki Sunao is a ronin (exam-prep student), who has recently oved into an apartment. He begins his new life living alone with a gloomy expression. However, after meeting the wife of the couple living next door and being captivated by her beauty, Saiki's new life begins to take on some color.

-I'm Ayano Shinonome, your next-door neighbor. Nice to meet you.

By coincidence, Saiki ends up working at the same part-time job as Ayano. As she kindly looks after him both at work and at their apartment building, Saiki gradually finds himself falling for her.

However, she is a married woman. Saiki tries to resist his feelings, but his love becomes increasingly difficult to suppress, leaving him caught in an ongoing internal struggle.

At the same time, Ayano begins to see traces of her first love in Saiki and starts to become conscious of him as a man...

The memory of a first love, the warmth of a married woman. Separated by nothing more than a single wall, a dangerous romance begins to blossom.