Just like every spring and summer, Naoki and his sister Noriko are visiting their aunt Mikiko and cousin Takashi in the countryside in the spring of Naoki's 17th birthday. With its courtyard full of various flowers alongside its kind residents, the family home is, in the siblings' minds, an idyllic utopia.

Naoki and Noriko's fantasies soon begin to crumble as tragedy brews around them. The gentle and kind Takashi, as if having turned into an entirely different person, becomes increasingly cruel and indifferent to his surroundings. As her son continues to spiral downward, Mikiko's anxieties take a turn for the worse.

Amid this dire situation, Naoki tries to delve deeper into his family's dark and tragic past, hoping to find the reason behind Takashi's sudden change and prevent a catastrophe from taking place.