Azai Nagamasa, daimyo of Omi Province, married Oichi, sister of Oda Nobunaga, in an alliance-sealing arrangement. Nagamasa experienced love at first sight upon meeting Oichi. He held deep respect for his brother-in-law Nobunaga and initially supported Oda campaigns, fighting in key battles like the defense against the Rokkaku clan at Kannonji Castle. Nagamasa's loyalty to Nobunaga clashed with his obligation to the Azai clan's longstanding allies, the Asakura, whom Nobunaga targeted for unification.

Pressured by retainers to honor the generational pact with the Asakura, Nagamasa betrayed Nobunaga during the Oda campaign in Echizen. At Kanegasaki, he feigned granting safe passage to Nobunaga's forces before launching a surprise attack. This betrayal stemmed from duty to the Asakura, not personal animosity toward Nobunaga. Subsequently, Nagamasa actively coordinated with the Asakura and other anti-Oda factions, including the Takeda clan, mounting resistance against Oda expansion.

The conflict culminated at the Battle of Anegawa, where combined Azai-Asakura forces suffered decisive defeat against the Oda-Tokugawa alliance. Besieged in his stronghold at Odani Castle and recognizing futility, Nagamasa committed seppuku. He first ensured Oichi's safe return to Nobunaga, entrusting her and their three daughters—Chacha, Ohatsu, and Oeyo—to his brother-in-law's care, underscoring his enduring concern for family despite political downfall.

In broader portrayals, Nagamasa's story occasionally extends beyond his historical death. Some narratives depict his unresolved regrets manifesting spiritually, where learning of his daughter Chacha's survival and impact allows him posthumous peace. His character consistently emphasizes duty, familial love, and the tragic consequences of divided loyalties during Japan's Sengoku period.