Reiko was a girl who had inherited numerous gambling debts from her father owed to a Yakuza hitman named Goro. He took her as his property to keep until his death; which he boasted could only be done at the hands of a dead man. Goro was eventually hired by a drug lord, Dai-Kumo, to kill Tyger Tiger's body guard, Patch (aka, Wolverine). Goro managed to "kill" Patch with a sword through the chest. When Patch later killed Goro, Reiko was free and very thankful to her benefactor.
Later, when Patch was fighting with Goro and Dai-Kumo's men, Reiko decided to repay her savior by killing Dai-Kumo herself. However, Dai-Kumo worked for the then leader of the Hand, Tsurayaba Matsuo. Matsuo was at war with Mariko Yashida; lover to the man Reiko knew as Patch. Instead of killing her for the death of his subordinate, Matsuo had Reiko blinded by removing her corneas. He told her that if she were to obey his orders then he would return her sight to her eventually.
In time, Reiko was sent out to kill Jubilee. When she learned of Jubilee's connection with Wolverine, she disobeyed her orders and let Jubilee go. Reiko tried to leave Japan, but she was captured by Silver Fox who was working for Hydra. Silver Fox offered to help Matsuo during his attack on Mariko's home by using "cunning, instead of brute force"; since the Hand ninjas Matsuo sent were being slaughtered by Wolverine, Silver Samurai (Mariko's brother) and Gambit as they fought alongside Mariko as she wielded the Honor Sword of the Yashida Clan.
Silver Fox sent Cylla to distract Wolverine while sending Reiko into the Yashida Stronghold under the guise of being an envoy for Matsuo to deliver a proposition. As Reiko made her way through a maze of razor-embedded walls and guard dogs with ease, Cylla encountered Jubilee and Yukio on the roof as they were looking for Wolverine to inform him of Reiko's capture by Silver Fox. When Cylla bashed a hole in the ceiling, Wolverine went to help his friends.
Reiko eventually came to the end of the maze and gave Mariko Matsuo's offer; allow him to buyout the Yashida Clan's underworld holdings "at fair market value so Mariko will not be profiting from vice"; a major source of contention in their war since Mariko's separating her Clan from dishonorable Yakuza business. However, for her behavior Matsuo wished for her to atone in the manner of the Yakuza - by cutting off a finger. Reiko offered a blade -coated in Blowfish toxin- given to her by Silver Fox.
The Silver Samurai didn't trust her and proposed that the blade was poisoned. To prove otherwise, Reiko plunged the blade into her hand; the others unaware that she had built up an immunity to the toxin over the years. Wanting the war to end, Mariko agreed to Matsuo's conditions and proceeded to cut off her pinky as Gambit protested. With only a single cut, Mariko felt a burning pain shoot through her arm as she cried out. Hearing her cry, Wolverine ran to her side.
When Reiko heard Mariko call Wolverine her "beloved", Reiko -who didn't know of their love- realized what she had done. Racked with guilt Reiko grabbed Silver Samurai's sword from his hand and said, "Is there no peace, other than the long darkness?", as she ran herself through; as Silver Fox had hoped she would upon learning the truth.
Mariko then begged Wolverine to use his claws to kill her; to save her from the pain and agony. The others in the Stronghold heard a single SNIKT! come from the Yashida Family chapel before he walked out carrying Mariko's body in his arms.