The Emperor of Nihon-Ja is the tenth installment of the Ranger's Apprentice book series by Australian author John Flanagan.

Months have passed since he was sent on a military mission to the court of the Emperor of Nihon-Ja with his friend, former wardmate and Scribeschool apprentice George, but he has failed to return.

Shigeru, though a Senshi himself, is also a man of the people and has been trying to reform his nation's strict social system, which Arisaka argues to be a betrayal of his class.

In an effort to buy them more time, Shukin and nine other Senshi volunteer to stay back at a river and duel the enemy until they are killed.

The men set up camp, and the Kikori begin refurbishing the fortress as more numbers join from the surrounding villages.

Unbeknown to them, Cassandra's party has arrived and begin their search for Horace, and are found by Kikori scouts and brought out to Ran-Koshi.

When they arrive on the other side, they make contact and find that the Hasanu are large mountain people covered in thick, reddish fur.

After learning of Shigeru's plight, Nimatsu insists that he wishes help, but the way is blocked by a forest haunted by a demon that has killed 17 Hasanu.

After killing it, they bring it back and disperse the Hasanu's fears, and they soon make preparations march for Ran-Koshi as the two girls finally come to understand one another and become friends.

Arisaka prepares to fight to the end, but Shigeru stops the battle, and says that he will give up his position as emperor if it will save hundreds of his people dying and leaving the choice of who will replace him in the care of nobles like Yamanda and Nimatsu.

As Arisaka charges the young Ranger, blinded with hate, Will hurls a saxe knife at his neck, killing him.