Rumors from Japanese industry insiders (via aniX chatter) suggest that Mokumokuren, the author, demanded an "exclusive animation" contract. This prevents the studio from outsourcing key animation frames to third-party foreign studios. It means the character acting—specifically the subtle twitches of Hikaru’s "thing" pretending to be human—will be drawn by in-house key animators.
Renowned animator Masanobu Hiraoka was brought on specifically for "Dorodoro" (slimy/viscous) animation, handling the complex body horror and the "insides" of the creature imitating Hikaru.
Fans are speculating that the studio attached (still unannounced as of the teaser, though rumors point to ( Mushoku Tensei ) or Cyclone Graphics ) is specifically known for "floor acting"—animating the space between dialogue, where the horror lives.
In the modern anime landscape, words like "exclusive" usually refer to streaming rights. For example, "Oshi no Ko" is an exclusive to HIDIVE. However, the announcement for The Summer Hikaru Died is different. The marketing materials specifically tout this as an – a phrase rarely used in the industry.
The series explores themes, as Yoshiki grapples with his grief and repressed romantic feelings for the real Hikaru while maintaining a dangerous bond with the creature that replaced him.