Nihon e Youkoso Elf-san.

Ms. Elf is intrigued by Japanese culture?!
Working adult Kitase Kazuhiro’s hobby is sleeping. Ever since he was a child, he’s had exciting adventures in the mysterious other world he dreams about. One day, while exploring ancient ruins with an elf girl he befriended, he is unfortunately burned by the breath of a magic dragon he encounters.
When he awakens from his dream, an elf girl who shouldn’t be in his room is sleeping next to him…
(Source: Crunchyroll)