Nihon e Youkoso Elf-san.

Kazuhiro Kitase's only hobby is sleeping. Ever since he was young, he would enter a wondrous world within his dreams and go on thrilling adventures. One day, he goes on an adventure with an elf girl he became friends with in his dream world, but it's put to an abrupt halt when they both get scorched with a dragon's breath! As he wakes up from his dream, he notices a familiar figure sleeping next to him...the elf girl from his dreams?! Join Kazuhiro on his new adventures through Japan with Ms. Elf!

(Source: J-Novel Club)