Suzuko Iseshima is the mother of protagonist Aya Iseshima. Years before the main events, she won the previous Martial Heart tournament. Her victory led directly to the defeated contestants, Kumi Honma and Yumi Kazuki, being sold into sexual slavery per the tournament's outcome.

This triumph established her formidable martial prowess, though she later retired from combat. Suzuko maintained a deliberate facade of normalcy, adopting a goofy, carefree demeanor around her daughter to obscure her lethal past and capabilities.

When Aya becomes entangled in a new Martial Heart tournament orchestrated by Kumi Honma and her children seeking revenge for Suzuko's past actions, Suzuko initially remains in the background. Her history directly fuels the antagonists' plot against Aya.

During the climax, Suzuko infiltrates the antagonists' hideout to rescue Aya. She confronts the primary conspirators—Miko Kazuki, Natsume Honma, and Haruki Honma—revealing their grandfathers' responsibility for the original tournament's corrupt structure and Kumi and Yumi's fate. When the trio attacks her, Suzuko swiftly dispatches all three by snapping their necks.

After ensuring Aya's escape from the burning building, Suzuko discovers the Martial Heart jewel fragments remain incomplete. She chooses to stay within the collapsing, fiery structure, her ultimate fate unresolved.

Suzuko personifies the reverberations of past violence, transitioning from participant in a brutal system to a figure seeking redemption through protecting her daughter, even at the cost of her own life.