Koyori Hoshi's heart was torn apart after her boyfriend suddenly ended their two-and-a-half-year relationship. To ease her misery, she finds herself drowning in alcohol, while whining and complaining to her childhood friend Hijiri Akiyama. Seemingly blacking out from the excessive drinking, Koyori wakes up to a bewildering sight, Hijiri and herself laying naked side by side. As she comes to her senses, the realization of her irreversible act with Hijiri starts to set in.

At first, Koyori thinks this occurrence is an attempt to rebound. Yet, the more she questions herself, the more she contemplates the affection she has harbored for Hijiri her entire life. After reflecting on their feelings toward each other, Koyori and Hijiri mutually agree to start their new life as lovers.

However, the two have always had a platonic relationship, and their bond never went beyond that. What effect will this have on the friendship they have built over the years? Honnou Switch follows the bizarre situation this newfound couple finds themselves in.