The Summer Hikaru Died, Vol. 1 is the first tankōbon of Mokumokuren’s Hikaru ga Shinda Natsuhorror manga. Translation is by Ajani Oloye.
Gloomy Yoshiki yearns for the day when he can leave his backwater hometown behind. Until that day comes, Yoshiki’s primary connection is his close friend, the endlessly cheerful Hikaru.
It’s just too bad for Yoshiki that Hikaru died during a hike up a nearby mountain and that the supposed Hikaru currently attending school with Yoshiki is an eldritch abomination wearing Hikaru’s reanimated corpse.