Elly is the Village's Shared Wife

The protagonist, Kyle (name changeable), and his younger sister, Elly, were attacked by monsters when they were young. Separated from their family by death, they were eventually taken in by a village in a remote frontier. Kyle resolved to become an adventurer to protect people from monsters, spending every day immersed in his training. His younger sister supported him from the shadows, almost like a mother would… When Kyle reached adulthood and announced he was leaving the village for the Royal Capital, Elly told him she would not go with him and would remain in the village instead… Time passed, and after a year of living in the Royal Capital, Kyle—having fulfilled his dream—returned to his hometown. But the sight that awaited him in the village was…