Yoshi Onagawa is a human lackey for the vampire Tujiro XIV. He often works with Niccolo Estes.
Yoshi is first seen picking up Anson Spar, the son of Christine Spar. Tujiro magically hypnotized Anson and had him walk out of his apartment, where Yoshi was waiting for him. This is the inciting incident that eventually leads Christine Spar to turn into Grendel. (Anson is apparently killed by Tujiro off-panel.)
Tujiro's troupe of kabuki players, who are also slavers, move to their next play in San Francisco. Christine Spar, who figures out that Tujiro is behind the kidnapping of her son, follows. In her new guise as Grendel, she spies on them and learns about their various routines. Yoshi, whom she nicknames the Shark, has a habit of visiting prostitutes at night.
Spar later breaks into their hotel and finds a grisly collection of dead boys' eyeballs, and realizes that Anson must have met the same fate. Tujiro, Yoshi, and Niccolo surprise her, and Tujiro tosses her out of the window. She survives, and follows up on a plan of revenge the next night.
She follows Yoshi to his nightly meeting with his call girl, and stabs him through the back of the neck with Grendel's fork, killing him. This is her first murder as Grendel.