She was the daughter of Shingen Harada, half-sister of the Silver Samurai, and cousin of Sunfire and Sunpyre. Upon her father's death, she had become head of Shingen's Yakuza crime family.

She met the X-Men when they had returned from a sojourn in the Savage Land and were asked to help Japan, which was at that time blackmailed by the terrorist Moses Magnum. She became Wolverine's fiancée, but their wedding was halted by the supervillain Mastermind, who had at that time been conducting a revenge campaign against the X-Men. He had used a mind control device to change Mariko's mind. When the control was lifted, Wolverine and Mariko resumed their relationship after a period of distance, but have not reconsidered marriage.

She was poisoned with tetrodotoxin by an assasin named Reiko, in the hire of her rival Matsu'o Tsurayaba in Wolverine vol. 2 #57 (July, 1992). She asked Wolverine to kill her to avoid a painful death. Wolverine killed her and vowed to avenge Mariko by yearly severing parts of Matsu'o's body on the anniversary of her death.

When last seen in Wolverine vol. 2 #175 (June, 2002), Matsu'o was missing an arm, his right ear, his nose and his gallbladder. He was planning to beg Wolverine for release through suicide. Wolverine never arrived since he was having a near-death experience in Canada. Whether Wolverine continues to honor the memory of Mariko by mutilating Reiko is uncertain.

An alternate version of her - as Sunfire, with the same powers as her Marvel Universe cousin - was a member of the Exiles from issue #2 (September, 2001) till her death in issue #37 (January, 2004. This version was created by Judd Winick and Mike McKone.