Kirara is a feline youkai.  One minute she is a cute little 2 tailed kitten, the next she can transform into a huge saber tooth feline which can fly on feet of fire.  She is very protective of Sango and now of the whole group as a newfound family.  Kirara is also much old and much more powerful than anyone realizes.  She was the companion of Midoriko herself, the creator of the Shikon no Tama.