The daughter of the owner of the casino cruise liner that Tsuzuki and Hisoka investigate. She has had heart problems ever since she was little, and has relied on treatment from Muraki, whom she has a crush on.
When she was little, she befriended a girl from Hong Kong named Eileen, who was a flower salesgirl. Eileen later boarded Tsubaki's father's ship, but then went missing. It turns out that Eileen was taken by Muraki, who extracted her heart and transplanted it into Tsubaki, who was not aware of any of this at the time. Eventually, Muraki told Tsubaki the truth, which shocked her greatly. He proceeded to hypnotize Tsubaki into thinking that Eileen's soul lived within her, causing her to develop a dissociative identity disorder, assuming the identity of Eileen from time to time. At the end of the King of Swords arc, she is shot by Muraki, which wounds her, but does not kill her. She then asks Hisoka to properly kill her, which he ends up doing by shooting her in the heart with the gun that Muraki had shot her with moments before.