Chomesuke is an Akuma that was modified by the Exorcist General Cross Marian prior to the events of D.Gray-man. Though still an Akuma under the control of the Millennium Earl, Chomesuke can repress his dominance for a limited amount of time and do as she wishes.
Her final mission is to bring a warning to the group of Exorcists (Lavi, Lenalee, Krory, Bookman, and Miranda) who are heading towards Japan in hopes of finding Cross. During the Exorcists' ocean battle with the Akuma, Sachiko keeps their ship floating by propping it up while underwater. Afterwards, she retrieves an unconscious Lenalee from the depths of the ocean and returns her to her friends. Although Sachiko is an Akuma, Timcanpy lands on her head, signaling that she has a connection with Cross. She explains to the Exorcists the peril of their upcoming journey. Despite this, they still decide to carry on.
With time against their side, she decides to push the ship to Edo, increasing their speed. Lavi opens a window and makes a remark that she is going really fast, calling her “Chomesuke.” Upon hearing this, Sachiko blushes, showing that she has some kind of affinity towards him; she decides to keep that name.
Once they arrive to Edo, Chomesuke takes on her human form, much to the surprise of all the Exorcists. Sadly, their guide, Kawamura, another modified level 2 Akuma, is captured and devoured before their eyes. Because of this, Chomesuke decides to take the Exorcists to Edo herself. On the way, she is captured by a level 3 Akuma and tells the group to leave her behind. Lavi saves her, saying that without her leading the way, all they will do is continue running away from Akuma. Soon, the Millennium Earl issues a powerful call to all the Akuma in Japan, a call much too strong for Chomesuke's will to withstand. Slowly, she loses control over herself, the desire to kill humans arising once more. Before completely losing her sanity, however, Chomesuke vows to help the Exorcists to the end and sacrifices her life so that the Exorcists may survive to confront a few Noah Clan members.