A lonely man (Tomoki) who apparently attracts bad spirits finds a ragged fairy (El) whose duty is to make him happy. Tomoki gets healed by El through cuddles and of course sex.
El ends up having to leave after accomplishing his goal but comes back when Tomoki is an adult thereby fulfilling his promise to be with Tomoki once he is a full fledged fairy
Yousei-san wa Yaritai Houdai