Leánnan sídhe (リャナン・シー Ryanan Shī) are a type of Faerie that consumes the blood of human and in return grants them great talent. They are typically carefree, viewing the exchange of blood for talent as a mutually beneficial exchange, and lack individual names on a whole. Redcurrant is an exception to this due to her infatuation with one lover in particular.
These vampires take on a humanoid appearance, much like normal humans with the exception of their pointy ears and ability to fly. They've so far only appeared as females with long slender bodies and clothing that often exposes much of their skin, such as their chest, neck and legs. Their personal appearance ties into their emotional state as well, so if one happens to suffer from emotional trouble their appearance becomes disheveled as well.
Longevity: A leannán sídhe can live for an extremely long time, even without taking in the blood of others. As such they can even lose track of time and remain motionless for extended periods.
Flight: A leannán sídhe has the ability to hover in the air and travel over long distances, much like the capabilities of humans way of walking. It's unknown whether or not this requires magic or if it simply comes naturally to them.
Intangibility: They are capable of passing through physical matter.
Inspiration: Leannán sídhe have the muse-like ability to inspire artists with their presence.
Life Draining: As a price for their inspirational presence, leannán sídhe drink the blood of their lovers, granting them great artistic ability but also slowly killing them. Leannán sídhe have no control over this ability and spending too much time with a mortal will slowly drain him/her of their lifeforce, whether she is aware or not.
↑Mahou Tsukai no Tsukai Manga — Vol. 3 Chapter 14,
Ruth explains their abilities.