Yamanaka Shikanosuke was born on September 20, 1545. In his art, his portraits conventionally show a crescent moon on the front of his helmet; he was born under a harvest moon. The crescent moon ornament he wore on his helmet was a token of good luck. Yamanaka was a Japanese samurai of the Sengoku period. He served the Amako clan of Izumo Province. During his warrior career, Yukimori supported the cause of Amako Katsuhisa, including the Siege of Kōzuki Castle. He even tried to get help from the Oda clan. Unfortunately, Oda Nobunaga only used him so the Oda army could march deeper into the Mōri clan's lands. Akechi Mitsuhide and Hashiba Hideyoshi wanted to give him reinforcements, but Nobunaga refused. Therefore, those two generals were forced into concentrating on laying siege to the Mōri and Ukita castles rather than helping Yukimori. By 1563, Môri Motonari had penetrated the borders of Izumo and was besieging the strategically vital Shiraga Castle. Yukimori was dispatched in relief with 200 horsemen and while he failed to lift the siege, he did distinguish himself for bravery. Further displays of his martial abilities would come in 1565, when the Môri surrounded Gassan-Toda, the Amako's headquarters. During the siege, Yamanaka's talents became well known even among the Môri, and a certain Shinagawa Daisen challenged him to a one-on-one duel.