Tatsu Toro's idyllic, but brief, marriage to her husband, Maseo, came to a sudden end in a single, tragic night. Her husband and his twin brother, Takeo, were both members of the Sword Clan, one of the clans in the Yakuza criminal organization. Takeo confronted his brother over a matter involving the clan, and in the struggle, Maseo was killed by his own sword, the Soultaker. This ancient Katana, one of the clan's relics, was said to contain the souls of those it killed, as well as possess other mystical qualities. Tatsu witnessed her husband's murder and collapsed by his body, overcome with grief. Takeo ran off into the night, and when Tatsu finally came to her senses, she took up the Soultaker and swore revenge against not just Takeo, but the Yakuza and all crime everywhere.

Tatsu is a woman wracked by grief and guilt. She goes by the name of Katana, in honor of the sword she wields and which is convinced contains her dead husband's soul. Due to this fact, she regularly has conversations with the sword, which is quite disconcerting to others. While she is a gifted swordswoman and martial artists, the sword can at time enhances her abilities in combat. When the sword is empowering her, the hilt of the sword glows with an unearthly light, burning Tatsu's hand.