Edited slightly to correct the problem with the wrong facing knee.
ARCO and IRIS are named after the Spanish for Rainbow. They are twins, and as their combined name suggests their powers are partly over light. Arco (the blue one) possesses greater speed than his sister and his dual form beam cannon can harness electro magnetic energy into lightning bolt like blasts. Iris (the purple one) has greater agility and also can teleport over short distances. Her dual beam weapon is keyed to harness electromagnetic energy into a light burst of laser intensity. They can combine the beams of both weapons to create a massive cross spectrum attack.
They were created originally to be one machine, but the power they were given was too much and split into two. They were specifically created to oppose CyberAgent Zero Returns, who was found to have gone rogue due to his programming becoming corrupted.
The split weapon design was taken from a mech built by kzt9, the technique used is different but the idea is very similar.