Zero, the children of the goddess of time, Rhinne, is a Warrior class in Maplestory and the Second addition to the RED Update.
Rhinne, the Goddess of time, anticipated the day that she would be imprisoned by the Black Mage so in a last resort, she forged a child named Zero. The Black Mage knew of the dangers Zero would bring so he ordered his commanders to split the child into two separate beings, one boy and one girl and to be banished into the Mirror World.
The boy, named Alpha, would serve under the Shadow Knights, an organization built to fend off the evils terrorizing the Umbra Temple outside of their hometown of Shadowvale. As time grew by, Beta grew suspicious of the Knights and what was inside the temple. His suspicions were truly confirmed when he realized that the Knights were guarding a young woman; his female counterpart, named Beta. The Knights grew wise of Alpha's actions and attempted to stop him from releasing Beta to no avail.
Beta escapes the temple with Alpha and the two teams up to know the Knight's true intentions and where they had really came from.
Zero brings a couple of special features not available to any other classes. For starters, Zero boasts a "two-in-one" mechanic in which allows you to either switch from Beta to Alpha or to have the two available in unison at the same time. Each character gives a different feel during gameplay and each have their own role.
Unlike the other classes, Zero starts immediately at level 100 instead of level 10 or 1. While this appears to be too good of a fact, Zero is only able to perform quests and level up in Mirror World much until level 180; they are able to travel to Maple World whenever they want, but they are unable to take quests, gain EXP or fight monsters or bosses until their storyline quests are finished, which is at level 180.
The class, like the Demon, Kanna and Angelic Buster, does not use MP but instead uses their own energy source called Time Force. Much like Demon Fury, Time Force can be obtained by attacking your enemies and can recharge over time.
On the matter of equipment, Alpha and Beta will share the same armor and accessories however because you play as both genders, they are unable to wear gender specific equipment. They can wear gender-specific Cash equipment as they don't share the same Cash inventory. They are also able to have their hair, skin and face changed independently as well.
As mentioned above, Zero allows you to play as either Alpha or Beta, each have their own roles in combat. The common mechanics they share is their ability to link their attacks, much like Hayato or Thunder Breakers.