Matsudaira Nobutsuna, a historical Japanese daimyo ruling the Kawagoe Domain during the early Edo period, first served Tokugawa Iemitsu as a page. Renowned for political acumen, he earned the nickname "Izu the Wise" from his court title, Izu no Kami. Appointed rōjū in 1633, Nobutsuna commanded shogunal forces to victory against the Christian uprising of the Shimabara Rebellion, suppressing Amakusa Shirou Tokisada. He later supported the underaged fourth shōgun, Tokugawa Ietsuna, alongside senior Tokugawa officials. Within the Edo Singularity of Fate/Grand Order, Nobutsuna plays a strategic role during Tokugawa Iemitsu's abduction and Kama's manipulation of the Ooku. Recognizing the existential threat to the shogunate, the monk Tenkai approaches him. They prioritize rescuing Lady Kasuga as essential to resolving the crisis. Tenkai sacrifices his life to cast a protective spell on Nobutsuna, transforming his organs into hanafuda cards imbued with energy matching Kama's Ooku. This spell also infuses Nobutsuna's soul with the conceptual property "one whose actions oppose the Tokugawa," enabling him to counteract Kama's false Tokugawa authority. Nobutsuna infiltrates Kama's forces under the guise of treachery, scattering his organ-cards throughout the Ooku to undermine her influence. Operating as Kama's subordinate, Nobutsuna attempts to recruit Yagyuu Munenori before Munenori's transformation into an Ooku pillar. He argues swearing allegiance to Kama—a victorious deity who toppled the Tokugawa—is pragmatic, citing historical defeats like Sekigahara and Osaka. Munenori consistently rejects these overtures. Nobutsuna later confronts protagonists invading the Ooku, deploying spectral entities against them while maintaining his cover. These interactions reveal Kama's objective: trapping individuals within a labyrinth designed to enforce depravity through violations of Buddhist precepts. Nobutsuna's physical and psychological state deteriorates as the narrative progresses. He appears on the fifth floor indulging in hedonistic pleasures with Kama's clones, a departure from his historical avoidance of alcohol and tobacco. He justifies this as irresistible compulsion, describing Kama's copies as transcendent. After combatants defeat his spectral guardians, he attempts to warn them against proceeding deeper but is overcome by coughing fits and retreats. In the labyrinth's innermost chamber, Nobutsuna assists Kama's efforts to convert protagonists into conceptual Tokugawa entities. His scattered hanafuda cards ultimately enable the protagonists to activate an Anti-Tokugawa shield, weakening Kama's constraints during their final confrontation. Despite this setback for Kama, Nobutsuna remains subservient, following her orders to monitor hostages like Goredolf Musik until the climax. In the alternate-history setting of Ōoku: The Inner Chambers, Nobutsuna appears as a secondary figure within the Ooku's political structure.