Lord of Miki Castle in Harima Province. He resisted Hashiba Hideyoshi's invasion of Harima, joined the Mori faction, and held the castle in a siege. He endured the siege tactic called "starving out Miki" — a prolonged blockade — and held out for two years from 1578 to 1580 before opening the castle and taking his own life in exchange for the lives of his garrison and family. He was twenty-two. His wife Teruko also took her own life to follow her husband. It is said Hideyoshi was moved by Nagaharu's noble end. The "Battle of Miki" is recorded in history as a model of Hideyoshi's siege-starvation strategy. As a young warrior who died for his people, he is still cherished in Miki City today.

A warrior with the pure sense of chivalry of youth and deep responsibility toward his people and retainers. His dignity in choosing death over submission embodied the essence of the samurai spirit of his time.

The Battle of Miki is recorded in Sengoku military history as a model of the siege-starvation tactic. The young lord's tragic self-immolation has been taken up in later literature and arts, and forms the core of Miki City's historical identity.