The Summer Hikaru Died (光が死んだ夏) is a Japanese manga series written and illustrated by Mokumokuren. It began serialization on Kadokawa Shoten's Young Ace Up website in August 2021. As of December 2025, the series' individual chapters have been collected in eight volumes. It follows the story of Yoshiki Tsujinaka, a teenager in rural Japan who discovers that his friend Hikaru Indo has been possessed by an otherworldly entity, forcing him to navigate their changed relationship amid supernatural dangers.
Mokumokuren first conceived of the series while studying for exams and later began posting drawings on Twitter, which led to the Young Ace Up editorial department approaching Mokumokuren to serialize the manga via the Young Ace Up website. An anime television series adaptation produced by CyPic aired from July to September 2025. A second season has been announced.
Upon release of the first volume, the series became a critical and commercial success, with the first volume selling 200,000 copies in three months and receiving critical praise for the story, artwork, and characters.
Plot
Yoshiki Tsujinaka and Hikaru Indo are two teenage boys and childhood friends living in a small town in rural Japan. Despite having opposite personalities and different hobbies, the two maintain a close friendship. However, on a winter day, Hikaru is fatally injured while hiking in the mountains alone. Before he dies, a mysterious eldritch being comes across him and consumes him, becoming him physically in the process. This "Hikaru" has all the feelings and memories of the original, yet remains a separate being, something Yoshiki realizes rather quickly. Yoshiki still wants to stay with "Hikaru"; however, his alien nature, along with other eldritch beings and hunters of said beings, may make that impossible.