The Summer Hikaru Died follows Yoshiki, a teenage boy living in a rural Japanese village, whose best friend Hikaru returns from a mountain hike acting strange. Yoshiki quickly realizes the being inhabiting Hikaru’s body is not his friend, but a shape-shifting, eldritch entity that consumed and replaced him. The entity, which now wears Hikaru’s face and memories, genuinely cares for Yoshiki in its own alien way, leading to a tense, bittersweet bond. The story explores grief, identity, and the horror of loving a monster. Readers enjoy it for its eerie atmosphere, emotional depth, and the unsettling contrast between the mundane setting and cosmic horror, as well as the poignant, queer-coded relationship between the two boys.