Irregular

Note: '''It is assumed for now that an Irregular forces open the doors of the Tower in order to enter the Inner Tower. It is unknown who or what teleports them into the Tower or even how teleportation functions outside of the Tower. This assumption that "Irregulars forcefully enter the Tower" will remain in its current form until more evidence appears to support or disprove it. '''

It is also unknown exactly what qualities are required to enter the Tower apart from possessing inner strength like determination, perseverance, bravery in the face of danger, etc.

In the current political system, under the contract Zahard made with a Guardian like Headon, 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". "

Politically, Irregulars are viewed as beings who have entered the Tower without being chosen. And it could be assumed they force open the door of the Tower.

However, before the current testing system was established, the original testing system of the Tower was likely created for Irregulars and thus, they are the true chosen ones. In ancient times, the terms "Irregular" or "Regular" didn't exist. The Irregulars are the ones who open the door of the Tower themselves, according to the Guardian of the 2nd Floor in Ch 58.

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

And in actual fact, 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 other qualities are required other than "true bravery", "true determination", "true perseverance", "certain combat qualities" 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 10 Great Warriors and Baam. They are then teleported by the Tower or a Guardian or a system within the Tower, into the Tower itself. After the door opens, they are teleported to the First Floor to take the Guardian's test (conducted by Headon). And only an irregular can visit the Guardian to request to take a Guardian's test (Ch 58).

Through all these Guardian's tests, they are tested repeatedly on the qualities they possess and chosen again at the top of the Tower to receive certain powers. However, it is unknown if Irregulars who fail to pass the Guardian's test are allowed to retake the test or are promptly disqualified.

All the known Irregulars that have entered the Tower are famous for being extremely powerful, and have wreaked havoc and terror within the Tower. Their mysterious ability to control and manipulate Shinsoo exceptionally well is also deemed abnormal by the residents of the tower, as Irregulars are capable of having more freedom in controlling Shinsoo even with the restrictions imposed by the laws of the Tower. It is interesting to note that all known Irregulars that have become Rankers have surpassed every single active High Ranker in just one act, Phantaminum storming Zahard's palace, Enryu killing a Guardian, Urek Mazino fighting toe to toe with Arie Hon then being deemed stronger by the latter. It is also interesting to note that none of the known Irregulars have the same position, possibly hinting at the creation of an elite team that could reach the top of the Tower.

Note: Under the current testing system established by the Zahard Empire, the key difference between Regulars and Irregulars is this. Regulars are chosen by Headon and then, instantly teleported to the Second Floor. However, Irregulars simply open the doors of the Tower and are then, teleported to the First Floor to take the Guardian's test (conducted by Headon). That is: they are "unchosen".

The Truth of Irregulars
Headon chooses the Regulars. But from current proof, Headon can choose the Irregulars. Irregulars aren't just Irregulars. There are three kinds of Irregulars: Note: The fact that Irregulars are strong is only applicable to those that forced their way into the Tower. This is because, Rachel, for example, did not possess the power to enter, but she got in while the door was open. It is believed that Irregulars are strong; and the majority of them are. But still, this is only applicable to those who forced their way in. This is because the Irregulars can only get in if they are strong enough to open the door. Therefore, the only ones that get in are monssterously strong.
 * Those who force themselves into the Tower; Phantaminum, Urek Mazino
 * Those who get let in by circumstance; Rachel
 * Those who are supposedly chosen by The Tower and Headon, but are used for reasons other than Zahard's desires; Viole (apparently, unconfirmed)

Zahard & 10 Great Familes
Although King Zahard and the 10 Great Warriors came into the Tower from the outside world in ancient times, this was before the testing system was invented. They are not considered as "unchosen Irregulars" because of this. However, they were still chosen by The Tower.

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 lacked certain qualities to be selected by the Tower.

Trivia

 * Irregulars aren't all deemed lethally powerful. Such as Rachel. It is just her namesake.