Mr. A is a Parasite who considers Shinichi a threat. Reiko calls him a fool while Migi describes him as "not one of our smart ones." Mr. A has no capacity for subtlety or deception, and no qualms about using his shapeshifting abilities in view of the public, reasoning that he can always get out of trouble by fighting, running away, and changing into a different face. Mr. A (or rather, his host body) is the father of Reiko's child. Shinichi is forced to battle Mr. A when he attempts to hunt Shinichi down and kill him at school. Though Shinichi and Migi badly wound him, they are forced to flee before he can be completely destroyed.
He is killed after their battle by Tamura Reiko for endangering her undercover lifestyle.