Warlord Yeshin is introduced in Book 2, Aina’s Breath. Warlord of the Oren-yaro lands, he was actually born the youngest son and did not know he would inherit the title until late into adulthood.
This meant that Warlord Yeshin grew up mastering skills meant to support his brothers–swordsmanship, archery, horseback riding, and soldiering. When he found himself outliving his brothers, he quickly took pains to educate himself, calling on scholars to help him learn how to rule.
As he rose to power, Jin-Sayeng grew to see Yeshin as a true representative of his people’s reputation: strong, dutiful, and steadfast. They also saw everything they feared of the Oren-yaro in him: aggressive, impatient, unforgiving, and with a penchant for recklessness. This made Yeshin an imposing figure, one to be wary of.
As of the start of Aina’s Breath, Warlord Yeshin is coming to terms with his second wife leaving him for another man. His first wife died of childbirth, but left him with four strong sons: Taraji, Senjo, Lang, and Shoen.
“Frightened of me, you mean,” Yeshin said with a snort. “I should have never gone through with those beheadings. Worked far too well, if you asked me.”
-Aina’s Breath
These guys, and more, in The Agartes Epilogues, the epic fantasy that pretends it’s a soap opera.