Senshi are the elite warriors of Nihon-Ja. They are like samurai in real life. In the book, The Emperor of Nihon-Ja, Arisaka, one of the main leaders of this group, started a mutiny, angry that Emperor Shigeru was trying to give common citizens equality to the Senshi.
The senshi are divided into clans, each represented by a symbol. The senshi clan led by Arisaka has the symbol of a red owl, and the one headed by Shigeru was a three cherry.