**Optimized Description:** Endō Naotsune served as a retainer to the Azai clan during Japan’s Sengoku period. He opposed the political marriage between his lord, Azai Nagamasa, and Oda Nobunaga’s sister, Oichi, viewing Nobunaga as a critical threat to the Azai clan. His loyalty drove him to request permission to assassinate Nobunaga after their initial meeting, though Nagamasa refused. At the Battle of Anegawa in 1570, Naotsune camouflaged his troops as Oda forces to infiltrate Nobunaga’s camp. The strategy was uncovered, and Takenaka Kyusaku—younger brother of Takenaka Hanbei—killed Naotsune as he advanced toward Nobunaga’s headquarters. Historical records credit him with slaying ten Oda warriors in this clash, reinforcing his fierce combat prowess. Beyond warfare, Naotsune donated an illustrated poem to the Taga-taisha shrine in 1569; this artifact remains preserved. In the *Ninja Girl & Samurai Master* anime’s third season (*Nobunaga no Shinobi: Anegawa Ishiyama-hen*), he appears as a historical figure visually depicted with a balding head, consistent with his role as a feudal retainer.