Shiraishi Kazuhisa, a former gokenin noble of the Kamakura Shogunate, lost his lands and title, resulting in exile to Tsushima Island. He arrived among prisoners conscripted to defend against the Mongol invasion. His noble background provided mounted combat skills and warfare experience.

Initially, Kazuhisa fought alongside Kuchii Jinzaburō and Tsushima's defenders, serving as a trusted lieutenant and second-in-command. His tactical knowledge and combat abilities proved vital in early clashes. However, disillusionment with Tsushima's fragile defenses grew. Influenced by fellow exile Obusuma Saburō, Kazuhisa betrayed the defenders, revealing their locations and strategies to the Mongols in exchange for a promise of restored noble status after Japan's conquest.

This betrayal caused significant losses, including the fall of Kokufu. Witnessing Kokufu's destruction sparked remorse, recalling the downfall of his own city. Despite this regret, he believed redemption was impossible and continued aiding the invaders. When his failures diminished his value to the Mongols, Kazuhisa sought a final duel with Kuchii. Mortally wounded, he accepted his fate calmly and requested execution. Before dying, he made Kuchii swear to protect Tsushima's people—a promise contrasting his own abandonment of that cause.

Princess Teruhi permitted his burial instead of displaying his head as a traitor, acknowledging his earlier contributions to Tsushima's defense.