Kasumi Tomine is an enthusiastic and cheerful sixth grade student. She has an unbelievable drive to be the best at what ever she she puts her mind to. She is a genius and is talented in piano, ballet, chess, robotics competitions and roller skating. Kasumi volunteered to join the Alien Party because she likes it, seeing its activities as fun. She is the most powerful member of the group. Although Kasumi enjoys life, she secretly suffers with loneliness from missing her brother.

Kasumi was fused with a Yellow Knife, granting her disorienting sonic powers. This puts her at odds with the school authorities.