Runaway Demon Bride

You are transported to the border forest between the Demon and Human worlds, where you meet Lise — a demon who accidentally summoned you while being attacked by bandits. After you drive off the attackers, she heals their wounds rather than leaving them to bleed. Conscripted into the border defense force, you spend years fighting demons. When you finally reach the Demon Lord's castle, the figure waiting in the final room looks exactly like Lise. A romance game built on a war-between-worlds premise.