An otherworldly being forms a mutual relationship with an ordinary human.
Do We Have This One? An ordinary person has an encounter with a strange creature, or maybe someone with special powers. The ordinary person allows this uncommon being to live with him/her and his/her family. Together, they experience several exciting escapades, which result in an Odd Friendship. The otherworldly being, in turn, learns more about humanity. If the ordinary person and the special houseguest have opposite genders, they might even engage in a Fantastic Romance. Trope Namer is the Platypus Comix article "The Platypus Comix Almanac of Special Houseguests".
Examples:Anime and Manga