Irregular

An Irregular is a being who entered the Tower by opening its' doors.

Current definition of an Irregular
In the current political system, Headon visits the Outer Tower and outside the tower to select Regulars(Ch 10). In this system, Irregulars are called "unchosen Irregulars" and regulars are called "chosen Regulars" or "selected chosen"(,Ch 2). It is unknown if this current selection process is part of a contract Zahard made with a Guardian like Headon.

Politically, Irregulars are viewed as beings who have entered the Tower and in turn, the Inner Tower, without being chosen by Headon. And according to Yuri Zahard, they're "probably not too welcome"(Ch 2) and she assumes Headon doesn't like Irregulars. And according to Ship Leesoo, Irregulars have "opened the door themselves of their own will" and that doing so goes "against the tower's laws"(Ch 58).

"Irregulars have all brought great chaos into the Tower"(Ch 58) and "all the people in the center of the Tower"(assumed to be the Ruling Class and many of those serving the Zahard Empire) tremble at them. Despite the laws of the Tower(presumably the Shinsoo contract binding Regulars and Rankers), all of them seem to have massive potential in the amount of Shinsoo they can control and are extremely talented at manipulating Shinsoo.

Most are known for notable acts like Phantaminum storming Zahard's Inner Palace, Enryu killing a Guardian, Urek Mazino fighting toe to toe with Arie Hon and then being deemed stronger by the latter. The exception is Jyu Viole Grace who has yet to perform a notable feat.

Original testing system
In ancient times, the terms "Irregular" or "Regular" didn't exist. The Irregulars are the ones who opened the door of the Tower themselves, according to the Guardian of the 2nd Floor(Ch 58). And likely, the term is a simplification of the entire process as one doesn't physically open the door of the Tower to enter it.

Since the current testing system had not been established then, the original testing system of the Tower was likely created for Irregulars and thus, they are the true chosen ones. The duty of the Guardians was to test these Irregulars(Ch 4) since likely, only Irregulars can be tested by them(Ch 58). And only Irregulars can climb the Tower(Ch 76).

Note: it is uncertain if the Tower was created solely for Irregulars alone as groups of people were living in there before Zahard's arrival.

How Irregulars are possibly selected
People who live in the land(s) outside the Tower are selected by The Tower if they meet a certain criteria. It's unknown what qualities are needed for a person to become a "chosen one". This is evidenced by the fact Headon told Rachel that "you're not the person the Tower has selected" and "you have not been chosen"(Ch 76). Although it is possible Headon or another Guardian is involved in the choosing of an Irregular, it's likely the Tower does the choosing and possibly, even the teleporting.

Examples of Irregulars include Zahard and the 10 Great Warriors and Baam. They are then selected by the "light" of the teleporting system and then teleported through the door of the Tower into the Tower itself. While they're being teleported through the door, they're still physically present in their current location(Ch 76).

The Guardian's tests
They are then teleported to the First Floor of the Inner Tower to take the Guardian's test (conducted by Headon). And only an irregular can request to take a Guardian's test (Ch 58). Take note that one cannot become a "chosen one" or an Irregular by participating in the Guardian's test, like Baam's group in the Submerged Fish Hunt test.

The Guardian's test reflects the "worth of the things"(Ch 4) the Irregular wishes to gain from the Tower and in essence, his desires(Ch 58). How precious are the things he wants which in turn, determines their worth to him? What are the lengths will the Irregular go to obtain his heart's desires and is he willing to undergo gruelling challenges to take the journey of fulfilling them at the top? And as he climbs the Tower, will he give up in the the middle of a test or after having passed numerous tests?

When the Irregular passes a Guardian's test, the Guardian will then grant his wish by teleporting him to the next Floor (Ch 4), except for Floor 43 because the Guardian is dead. But if they fail or give up while taking the test, they may not pass and they may not ascend to the next Floor. It is unknown if Irregulars who fail to pass the Guardian's test on a certain Floor are allowed to retake the test or are promptly disqualified from climbing the Tower.

It is supposed that when an Irregular reaches the top of the Tower, he is then chosen again to receive certain powers. "As promised, all that you seek, all that we desire, is prepared up there. On top of the Tower" (Ch 78).

Known Irregulars

 * Baam (Wave Controller)
 * Phantaminum (Exis)
 * Enryu (Spear Bearer)
 * Urek Mazino (Fisherman)
 * Rachel (Light Bearer) Politically, Rachel is known as an "unchosen Irregular" but to the Guardians, she's most likely not a "chosen one". This is because she was not selected by the Tower.