In this world there are two distinct classes, the upper class being generally bigger and faster than the lower and magicians belong to the upper class regardless of their race. Magicians can access an another dimension that demons exist.
The first book starts with the main character aiming for admittance in a school for warriors at the same time his/a girlfriend is found out to be a magician which puts her in a different social class than him. he convinces a famous lower class warrior to admit him into his group
As he gradually trains with this group he dedicates himself completely and progresses quickly until he as a dual wielding swordsman and is better than all the upper class cadets.
The magicians can cast a beam of light that transports people to an alternate reality overlying their own, where demons live. In this world these demons kill you, but when the beam of light is stopped you return to your body as if nothing has happened. They use this to disable their enemies. The lead character gets access to this world and to improve his swordsmanship he enters this world to train while every else is asleep, dying over and over again to try and be the best.