Kimi to Boku no Saigo no Senjou, Aruiwa Sekai ga Hajimaru Seisen

Summary

The Empire endowed with an advanced level of knowledge, and the Nebulis Imperial Household Agency feared as the 'Country of Witches.' On the long-lasting battlefield between these two countries, a boy and girl met. The ice witch princess praised as the strongest in all of the Imperial Household Agency―Aliceliese. The swordsman who became the ultimate force on the battlefield at the youngest age throughout all the Empire's history―Iska. "If you capture me, your dream may also be fulfilled." "Likewise, if you defeat me, it will become a step in the unification of your world." The two arch enemies were to kill each other. However, the boy had his heart stolen by the girl's beauty and nobility. And the girl was attracted to the boy's strength and way of living. Even if walking alongside one another would not be permitted and the only path before them was to defeat each other. (Source: Novel Updates)