Head of the Anbu Division [Avatar of Hell]
Soisne is the head of the Anbu hunter ninja division of the Shattered Sky Village and is directly responsible for the maintenance or Arashi Totaro and making sure he is kept in check. She works directly under Saigo Uchiha and thus is slightly more lenient with Arashi than she necessarily should be. She openly allows people to use her moniker, The Avatar of Hell.
Her known jutsu allows her to manipulate blood, the only time the players have seen this type of jutsu from her was when the first lesser greed demon was revealed. She, took our two city blocks with her jutsu and absorbed their blood to create a giant suit of blood armor that formed into a giant person to fight the demon. This jutsu apparently makes her close to invulnerable.
She also seems to have some association with Arashi and his past, although it is unclear what this connection is.