Tenkai Knights, Go!

Tenkai Knights, Go! is a paperback by Brandon T Snider. It was published on September 25, 2014.

Official Description
And two more makes four.

Guren and Ceylan are doing fine on their own, until they learn of two other boys with the ability to become Tenkai Knights! Chooki and Toxsa don’t seem to be allies at first, but Guren and Ceylan soon learn to trust them. But will they manage to achieve a victory together?