The Emperor of Nihon-Ja by John Flanagan
To learn more about different battle skills, Horace travels to Nihon-Ja to learn the ways of the Senshi warriors. While he is there, he becomes good friends with the Emperor. But when a rebel Senshi threatens the emperor's power, Horace must choose between safety and protecting the emperor. Loyal to his new friend, Horace stays.
When Will and Halt get word that Horace has stayed in Nihon-Ja to protect the emperor, they rush to help him. Soon, the Araluens find themselves caught in a battle between those loyal to the emperor and the rebel Senshi warriors. With limited troops and resources, the emperor cannot hope to win, unless the Araluens are brave enough to find help.
The Senshi arrow flashed downward, heading directly for the emperor. Will flicked his bow at it, caught it, and deflected it from its course. The arrowhead screeched on the hard, rocky ground and the arrow skittered away. Even Halt took a second to be impressed.
"How did you do that?"
Then, realizing that there was no more time for talking, he shot the Senshi bowman.
**Book 10 in Ranger's Apprentice**
Previous book: Halt's Peril