Invited to walk around the culture festival together by Shirogane, Kaguya is unable to hide her surprise at this sudden plot twist. She lightly joked that maybe he was affected by the festival's atmosphere, but Shirogane never dropped his serious expression. Compelled by such intensity, Kaguya decided to walk around the school together. Everyone around them gossips that they are on a date as Kaguya blushes. But while they enjoy visiting a love fortune-teller, food shops and live music, Kaguya feels true happiness. From the depths of her heart, she wishes that each day could continue just like this.

The moment the culture festival reached its finale, the jewel object made by Shirogane was stolen by a phantom thief who calls himself Arsène. Kaguya and the others headed to the roof where the phantom thief keeps appearing, but there was no one there. Fujiwara, who transformed into a genius detective, struggles to solve the mystery behind the calling card and uncover the thief's true identity. But Kaguya, left behind at the scene of the crime, had begun to figure out the criminal. The problem is the location. Kaguya traced the phantom thief's line of thinking and headed to where he is now...

Shroud in a cape and dressed in the guise of the phantom thief Arsène, Shirogane waited for Kaguya's arrival atop the clock tower roof overlooking Shuchiin. When asked why he would do such a thing, Shirogane answered that there was something he wanted to show Kaguya. The festival's afterparty has already begun as the sun set over this school and the students could be seen encircling and enjoying the bonfire. While the emotions that could not be expressed with words mingled between Shirogane and Kaguya's hearts... Shirogane carried out his ultra-romantic operation!!