Shokei Sareta Saikyou no Gunnyou Majutsushi, Haisenkoku no Elf Hime to Kokka Saikensu ~Sokoku yo Jama Suru no wa Kattedaga, Sono Majutsu Tsukutta no Ore na Node Kikanai ga?~

Read Manga 処刑された最強の軍用魔術師、敗戦国のエルフ姫と国家再建す～祖国よ邪魔するのは勝手だが、その魔術作ったの俺なので効かないが？～ / The Executed Strongest Military Magician Rebuilds His Country with the Elf Princess of a Defeated Country?

The magical nation of Ingressa came to dominate neighboring countries with the power of groundbreaking military magic. Supporting this dominance from behind the scenes was Hert Eisenheim, who rose to the rank of archmage at a young age. However, due to a scheme by the court magician who was jealous of his talent, Hert was executed as a war criminal – but when he woke up, he found himself summoned before a young girl. The girl’s name was Iris Refrain, and she was the first princess of the elven kingdom that he had destroyed.