Red Art is one of the easiest of the four to learn yet still complex enough to master. In order to fully master the craft you must be able to merge with other arts. Essentially it is require you learn other art in order to master the Red Art, but it not required. Most of the more technial Red Remiens are able to combine other people art to form a more powerful attack. One of the most common skill is combining a Black Remien's Pyro with their weapon like a sword to create Pyro Slash. Red Arts mostly consist of abilities to upgrades their stats like Agility, or strength while lowering the enemies.
Once they advance further in their skills, they can learn more offensive skills that can damage the enemies while possibly inflicting abnormal status.