Masuka is the Miami Metro Police lead forensic science investigator; he works alongside lead character Dexter Morgan in the lab and at crime scenes,[1] and is known for cracking tasteless and inappropriate jokes, invoking his Japanese heritage only when convenient, and harboring unrequited desire for Dexter's foster sister Debra.

However, his disappointment at this quickly evaporates when Debra and others defend his assessment of a crime in front of the doubting agents from another enforcement agency by suggesting that Masuka has been published multiple times.

He is attracted to one of his female interns, but ends up firing her when he finds out she stole evidence from the Ice Truck Killer case (a prosthetic forearm and hand) and sold it online.

In the seventh season, however, he quickly learns that Louis was the actual buyer of the stolen prosthesis when Dexter mails it back to Miami Metro with a letter of complaint.

In the novels, Dexter views him as a kindred spirit, believing that Masuka is also "pretending to be human", and asks him to serve as the best man at his wedding.