The Empire of O'ltormea, a militaristic country, summoned Ryoma Mikoshiba, a high schooler from another world. Dealing a major blow to the empire, Ryoma escapes their clutches. With the twin sisters Laura and Sara at his side, Ryoma meets a mercenary group called the Crimson Lion.

In the middle of mercenary work, Ryoma accidentally becomes involved in the inner workings of the Kingdom of Rhoadseria. Now forced to employ his wit and cunning in this world, Ryoma makes a pledge.

"I'll take it back, no matter what - the fate that's been stolen from me!"

The Rhoadseria Civil War arc, which marks Ryoma's first progress towards supreme ruler, begins!