During their beachside summer camp, Chihaya and her companions bask in the sun and waves, unaware of the emotional undercurrents surrounding Nami Minami and her unspoken affection for Natsuki. As Nami's inner shadows deepen, she ventures to an old mansion and discovers the Netherworld Tree, which seems to respond to her turmoil. This fateful meeting ignites the initial stages of a disruptive incident that begins to ripple through the group. Tensions mount as mysterious influences start to alter their carefree vacation.