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Yajiro Kojima is a swordsman also known as the "Rearguard Tiger" or "Tiger of the Rearguard", who battles in an attempt to bring about world unity. He is called the Tiger by Templar because the more cornered Yajiro becomes, the greater his abilities become. A former rebel, he was working as a mercenary until he met Rushuna. Although Yajiro disdains the use of firearms, he is skilled enough to parry bullets with his sword as well as slice massive cannon shells in two. Yajiro hates guns because he believes that gunners see the weight of a person's life in how hard it is to pull the trigger. However he later states that he does not see Rushuna in the same light as he does other gunners. The route that he, Rushuna, and Mikan take towards Tento's capital by crossing Mt. Charanbo and then White Wizard Lake retraces the same route that he followed when he was with the rebel army that attempted to invade the capital a year and a half ago and is thus memory-laden for him. Rushuna calls him "Yatchan" , an informal name he is initially irritated with, but grows to accept. Not too far into the anime, Yajiro seems to hint having some feelings towards Rushuna, evident on numerous occasions where he either gets embarrassed by her words, protects her without saying why, or shows jealousy towards her almost sisterly relationship with Mikan.
In the manga, he belonged to a branch family of the Kojima clan. This clan was led by Midare Kojima and his sister, Suguna. Yajiro intended to go out and make a name for himself, ensuring the safety of his village. While on a journey, Suguna gave her life to save Yajiro's own.
After the events in Volume 7 of the manga, Yajiro is said to have never lost a fight after that. He and Rushuna go on to get married.