"Summer Time Rendering" is a supernatural mystery thriller set on the remote island of Hitogashima. The story begins with Shinpei Ajiro, a high school student, returning to his hometown after the sudden death of his childhood friend, Ushio Kofune. Ushio drowned while saving a young girl, but her death raises suspicions due to its unusual circumstances. Shinpei reunites with Ushio's family, including her younger sister, Mio, and begins to uncover unsettling truths about the island.

Soon after his arrival, Shinpei experiences strange phenomena, including visions of Ushio and encounters with shadowy entities known as "Shadows." These creatures mimic the appearance and memories of the people they replace, posing a grave threat to the island's inhabitants. Shinpei discovers that he has the ability to "loop" back in time upon death, allowing him to relive events and gather information to combat the Shadows. With each loop, he uncovers more about the island's dark history, the origins of the Shadows, and their connection to a mysterious ritual tied to the Kofune family.

As Shinpei delves deeper, he allies with Mio and other island residents, including Hizuru Minakata, a researcher investigating the Shadows, and Tokiko Hishigata, a woman with her own agenda. Together, they work to unravel the conspiracy surrounding the Shadows and prevent the impending catastrophe threatening the island. The narrative is driven by a blend of suspense, action, and emotional stakes, as Shinpei struggles to protect his loved ones while grappling with the moral complexities of his time-looping ability.

The story explores themes of identity, memory, and sacrifice, with the Shadows serving as a metaphor for the loss of self and the fear of being replaced. The island's folklore and the Kofune family's legacy play a central role in the plot, intertwining with the characters' personal struggles. As the mystery unfolds, the line between friend and foe becomes increasingly blurred, culminating in a high-stakes confrontation that tests the limits of Shinpei's resolve and the bonds between the characters. "Summer Time Rendering" combines intricate plotting, well-developed characters, and a richly atmospheric setting to deliver a compelling and suspenseful narrative.