Colonel Merthophan Dextro instructs at the Azami military academy, presenting a calm demeanor and youthful appearance marked by short silvery hair and a scar beneath his eye, always clad in standard military attire. He scouts promising students like Lloyd Belladonna, whose talent he swiftly acknowledges, enforcing strict discipline under his personal motto: "Take care of discipline."

Driven by vengeance for his destroyed village, Merthophan manipulates political events to instigate war. As part of this scheme, he participates in cursing Azami's king, only to fall under the control of Abaddon, the demon lord possessing the monarch. This manipulation complicates his motives and deepens his antagonism. Following Abaddon's defeat by Lloyd and allies, Merthophan faces scrutiny and sentencing.

For his redemption, Merthophan is sent to labor near Kunlun village under Alka's supervision. He abandons military life for farming, a stark shift from his earlier ambition. This resolution contrasts his past willingness to sacrifice all for vengeance with a reformed existence, illustrating an arc from antagonist to a figure seeking atonement through agricultural toil.