The episode delves into the emotional fallout of past events, primarily from Nao's perspective.
In the present day, Nao visits the Kasugano residence under the guise of bringing mosquito repellent for Sora. However, her true intent is to navigate her rekindled relationship with Haruka while dealing with the jealousy and animosity of his sister, Sora, who is "consumed with hatred" regarding their proximity.
Nao is driven to explain her past actions and a specific "sin" she committed years ago when they were younger. It is revealed that she previously had a physical encounter with Haruka during a summer visit, which has deeply influenced her current feelings of guilt and devotion toward him.