Kagura

The Slayer of Yoma, Kagura's sole purpose in life is to kill and purge every last yoma from existence. She reincarnates every one hundred years to perform a 'cleansing' of the yoma in the world, before dying in a massive explosion to start the cycle all over again.

Kagura is single-minded in her pursuit to purge yoma, but she's not a complete drone. In her child form she is naive, innocent and playful. In her adult form, she is more serious and and fierce and her power grows, perhaps a little sadistic as well, but since she's fighting literal world-ending demons, she can have that much.

Kagura is the most powerful character in the series, capable of flight and teleportation while being able to tear into reality itself and bend time and space to her will. She has yet to be truly rivaled.

She also cares deeply for Naraku, her protector, and it's implied she may have romantic feelings for her.