Fairies are minor denizens of the realms of the Faerie. They are witness and simplistic, considered amongst the lowest of all beings. They resemble the typical appearance of fairies in legends, with butterfly wings and such. Taking on one as a familiar is seen as a stupid thing to do.
↑“I can talk, if it helps,” he said. “You were talking about Faerie. Court Faerie deal with prominent families and powers. Around here, you’re not getting a Faerie familiar unless you’re a member of the Duchamp family. You could get a fairy, that’s F-A-I-R-Y, but then you’re talking about the witless, minor denizens of their realm. Foot high things with butterfly wings. Going that route would be dumb.” - Excerpt from Breach 3.5