The Summer Hikaru Died (Japanese: 光が死んだ夏, Hepburn: Hikaru ga Shinda Natsu) 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 July 2025, the series’ individual chapters have been collected in seven tankōbon 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 CygamesPictures premiered in July 2025.

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.