The baby of the three is Aki. She can be beaten easily if you know exactly what to do.
The Kotodama allows Aki to create any kind of illusion. It can also be very dangerous for the reason that if one truly believes that what he/she sees is true, then he/she will hurt himself in someway for real.
Weapon: Idaten and Yamabiko
Miki is probably the girl with the coolest outfit in this animé. I really believe that she could not win a fight without her sister Nayumi.
You can move in an unbelivable speed if you have Miki's Idaten, which is located in her boots. Nayumi's Quartet attack is not possible without Miki. The Yamabiko Miki has reflects all kinds of energy including sound waves and can also be used as a shield.
Name: Nayumi [Neon]
Weapon: Fukyu Waun
Nayumi, together with her two sisters, was a maid in Kurei's mansion before becoming a member of the Uruha (Jushinsu to be exact). She fell in love with Kurei and decided to be loyal to him even if it would cost her life.
Nayumi's magical weapon is a crystal ball located in the torso of her costume. It uses sound waves as a weapon (Cool, huh?).
Note: The flute she uses is definitely not her elemental weapon. It is just used to materialize the sound waves and sometimes to protect herself from other sharp weapons.