Yui

Yui is intellectually curious and openly excited by the opportunity to examine a completely unknown organism.

He approaches the Parasites primarily as a biological discovery. His enthusiasm during the examination contrasts with the fear and uncertainty felt by officials trying to understand the threat.

Yui also expects the investigators around him to follow some of his biological reasoning, occasionally overestimating their scientific knowledge while explaining his findings.

Yui is an ordinary human without supernatural abilities.

He is an accomplished scientist capable of dissecting and analyzing Parasite tissue. His examination reveals important information about how Parasite cells differ from ordinary human cells.

Most importantly, Yui determines that detached Parasite tissue reacts differently from human tissue. A strand resembling hair taken from transformed Parasite tissue will lose its structure and revert into living Parasite cells, creating a simple potential identification test.

Yui is contacted after Hideo Shimada's body becomes available for scientific examination.

His autopsy gives the authorities their first opportunity to study a complete Parasite corpse under controlled conditions.

Yui's findings help investigators understand that even apparently ordinary structures produced by Parasite tissue can reveal themselves once separated from the main body, contributing to the development of methods for identifying hidden Parasites.

Hideo Shimada provides the Parasite body that Yui examines after the school incident.

Shinichi Izumi is part of the wider phenomenon being investigated, although Yui's principal contribution concerns Parasite biology rather than a close personal relationship with Shinichi.

Migi belongs to the species whose unusual cellular properties Yui studies.