About the size of a butterfly yet as loud as a dragon, pixies were once believed to be a form of fairies but are truly the furthest thing.
Yes, they may look identical but smaller, but where fairies use their magic to help, pixies use their magic exclusively for selfish reasons. Selfish yet harmless.
Pixies like fairies feed off magic, meaning they have no need for The Union, no need for society or any of that. Pixies exist only to cause chaos and have fun, usually this chaos means things like leading an army of butterflies into a classroom to distract students from learning history or giving the wrong directions to a hiker leading him into an elven village where the elves will roll their eyes and guide him back to society.
Nobody expected them to join The Union but King Valentine saw Pixies as the perfect addition to a growing kingdom, offering them tools for their games in exchange for leaving the serious elves alone. Valentine also taught them to play their pranks on children who were easier to trick, but also usually enjoyed the pranks just as much as the pixies.