As Shinichi and his parasyte continue their unasked-for coexistence, the parasyte in his right (migi) arm decides to take on the name of "Migi." Shinichi realizes that parasytes are involved in the ongoing mincemeat murders. Feeling alone in his discovery, Shinichi grapples with frustration. Unbeknownst to him, he is about to meet another parasyte for the first time...

As the number of mincemeat murder victims grows, Shinichi, alone in his knowledge of the truth, is in turmoil. When Migi suddenly alerts him to the presence of another parasyte, he is aghast to find that it is in his own school. Paranoid, Shinichi attends a schoolwide assembly, where the staff introduce a beautiful new teacher...

Shinichi's life returns to "normal" after A's killing spree, but Shinichi remains in low spirits. His mother, Nobuko, becomes worried, but Shinichi just bluffs when she asks him what's wrong. His father, Kazuyuki, suggests to Nobuko that a past incident may be involved. Nobuko looks down at the old scar on her hand and thinks back to what happened when Shinichi was a little boy...

Struck through the heart by his mother-turned-parasite, Shinichi survives only through Migi's efforts. After regaining consciousness, Shinichi is devastated by the realization that none of it had been a dream.

Shinichi has regained some semblance of a normal life. However, with Migi's cells dispersed throughout his body, his physical abilities have greatly increased to the point that not even Mitsuo poses a threat. Shinichi fears that the changes go beyond the physical and into the psychological. Just as peace returns to his school, a new parasite appears!

Incapable of rationala thought, Shimada Hideo is a savage beast on a rampage, and Satomi's class has become his prey. Shinichi must make his way through the carnage in order to save Satomi...

A few days after Kana's death, things seem to be back to normal for Shinichi. Satomi and her friends are perturbed by his seeming indifference, but Shinichi, himself, is grappling with his own sense of disquiet with his unnatural state of mind. Meanwhile, a man begins snooping around about Shinichi...

Suspecting Shinichi's connection to the parasite cases, Hirama arranges to have Shinichi meet with Uragami, a convict with a peculiar ability. Although cleared of any suspicion and able to return to his high school life, it isn't long before Hirama appears once more before Shinichi. A government operation to neutralize the parasites with Hirokawa is about to begin...