As a teen in her native , Cassandra Chao got involved in - and won - a lot of fights. Eventually this skill attracted the attention of the wrong people. A gang kidnapped her and forced her into working for them. They gave her (and numerous other minions) the coil exoskeleton armour and forced her to train in its use under threat of death.
She was sent on numerous missions, mostly petty theft. One of these went wrong and Cassandra was believed dead. Taking her chance to escape, she fled the country to seek refuge in America, taking her coil power armour with her and continuing a life of crime. She first encountered Acrobat during a bank robbery where he failed to stop her. They encountered each other again in their civilian identities at High School and recognised each other by their voices. They mutually agreed to keep each other's secret.
Coil was later hired as part of a group of supervillains to defeat Acrobat. They successfully defeated Acrobat, but when it became obvious they were going to kill him in cold blood, Coil balked, fighting off her erstwhile teammates and rescuing him.
Coil and Acrobat became closer over time. She began to assist him in crimefighting and they became romantically involved.
The arms and legs of the Coil exosuit are flexible and extensible to many times their apparent length. Coil is thus able to punch and grab from a great distance away as well as extend the legs to use as stilts or springs.
In addition to the abilities granted by the suit, Cassie is a superb martial artist. Even without her exosuit, she has proven capable of fighting off a group of trained opponents armed with Coil exosuits of their own.