Elf Yome to Hajimeru Isekai Ryoushu Seikatsu  

Life as the Lord of Yngling with the Elven Bride, エルフ嫁と始める異世界領主生活, エルフ嫁と始める異世界領主生活

Yuta, an orphaned teen, has a cute childhood friend and they live on the remote and mostly isolated Japanese island of Aoga. One day he encounters a strange fog and meets an apparent elf cosplayer.(Source MangaUpdates)