According to the ancient records in the Kojiki and Nihonshoki of ancient Japan, Nagasunehiko was the younger brother of Abihiko and the chieftain of ancient Yamato. When Emperor Jimmu started his migration east, he put his older brother Itsuse no Mikoto in command of the army. As the army approached Naniwa (where modern day Osaka now stands) they encountered the forces of the local chieftain, Nagasunehiko who showed his excellent leadership skills by defeating Jimmu's army and killing Itsuse in the ensuing battle.
Jimmu came to the conclusion that the reason they had lost is because they battled eastward against the Sun, and thus could not obtain the blessings of Amaterasu. He then decided to land on the east side of the Kii Peninsula so that he could battle westward, and with the help of Yatagarasu was able to move onto Yamato. While there, his army once again encountered Nagasunehiko's forces, but this time were victorious and was able to meet Nigihayahi no Mikoto who Nagasunehiko was protecting. Jimmu and Nigihayahi both claimed to be descendants of Takamagahara, and when the two met Nigihayahi accepted Jimmu's legitimacy, and Jimmu ascended to the throne.
"Origin: Japan. The ruler of Yamato no Kuni. He rebelled against Jinmu's conquest when the Emperor reached Kawachi. He repelled the Jinmu army twice, but was eventually defeated. Some say he died there, while others say he escaped and created a dynasty at Tsugaru."
—Shin Megami Tensei A-Mode DDS Dictionary
Devil Summoner: Raidou Kuzunoha vs. The Soulless Army
"The king of ancient Yamato. He is Abihiko`s younger brother. He fended off Emperor Jimmu and his migration east, but lost when Amaterasu aided the Emperor`s army."
—Devil Summoner: Raidou Kuzunoha vs the Soulless Army Devil Chart