Nako Kagura is a girl skilled in playing the cello. One day, she and her friend Iruka go down an underground cavern, which has a statue containing Steel Angel Kurumi Mark II!

Kurumi is released from her capsule and kisses her new master who just happens to be a girl... the girl's mother welcomes Kurumi with open arms and helps her get an outfit for Kurumi shall be joining her new master at school, which someone close to Nako isn't happy about.

Kurumi and Nako arrive (late) to their new school. The two's odd relationship gives them unwanted attention, especially when Uruka's dad sends a robot after Kurumi!

Uruka's dad discovers a Steel Angel like Kurumi named Saki. Uruka snoops around Nako's house to find the manual on how to activate Steel Angels.

Now that Steel Angel Saki Mark II has been activated, Uruka tries to make her fight against Kurumi.

Kurumi and the gang spend summer at the beach. But Uruka sets a trap for Kurumi in the water.

Kurumi and Uruka worry when Nako is late for dinner. Meanwhile, many practitioners attempt to awaken the next Steel Angel, Karinka Mark II.

Saki tries to get Kurumi and Uruka to be with her, but ends up being used as bait set up by the newly-activated Karinka Mark II.

Kurumi finds herself fighting the powerful Steel Angel Karinka.

Kurumi and Karinka get in an argument and accidently break Nako's cello. So, while Nako practices her cello skills with many other cellos at Uruka's house, Kurumi and Karinka get part-time jobs to buy a new cello for Nako.

Nako's cello contest is coming soon, and if Nako wins, then she will get to study abroad in Vienna. Kurumi and Karinka contemplate on how to feel about Nako going away. Meanwhile, Uruka persuades her father to use a special suit to prevent Nako from leaving her.

Can Kurumi keep Karinka and the battle-suit-equipped Uruka at bay and make it to the cello contest before Nako's turn comes up?