Nihon e Youkoso Elf-san.

Serialization of the Syosetu web novel with the same title.

Kazuhiro Kitase's main hobby is sleeping. Ever since he was young, he would enter a world within his dreams and go on exciting adventures. As he grew older, he became acquainted with a female Elf and the two have now been united through a Dragon's brand! As he wakes up one day, he notices a familiar figure sleeping next to him...the Elf girl from his dreams?! Join Kazuhiro on his new adventures through Japan with the lovely Ms. Elf!

(Source: J-Novel Club)