Kurumi is the first Steel Angel, and she is awakened when Nakahito kisses her. Nakahito is the second child of Onmyoudou Shuke (a house of a Japanese Yin and Yang spiritual leader).

Kurumi has so much affection for him that she calls him "my master", and only follows his orders.

Now, Nakahito, a boy with a gentle heart, and Kurumi, an android with an Angel Heart and incredible power, join forces.

When the second Steel Angel Saki, the third Steel Angel Karinka appear, things really start to mix up...