|“||The Tower doesn't open its gates for just anybody. No matter what, it only opens its gate to 'something' that it needs. Stability, Change, Revolution or Liberty...||”|
An Unchosen Irregular (비선별인원, 非選別人員, biseonbyeolinwon; "members who have not been chosen" or "Irregulars"), more commonly known as simply an Irregular, is someone who was not selected from within the Middle and Outer Towers to climb the Tower through Headon's normal selection of Regulars, but who entered the First Floor from the outside.
Nature and DefinitionMost neutrally, an Irregular is one who was able to enter the Tower on their own, by whatever means and for whatever reason. This grants Irregulars certain benefits, such as the ability to use shinsu without Guardian approval. Conversely, all other people in the tower did not 'enter' the tower themselves and are so restricted; they must be allowed to use shinsu and are bound by the laws the Guardians set down, such as a complete inability to kill King Zahard or a Guardian.
In the current political system, Headon visits the Outer Tower and the Middle Area to select Regulars. In this system, Irregulars are called "unchosen Irregulars" and Regulars are called "chosen Regulars" or "selected chosen". It is assumed Headon's choice reflects the Tower's choice and in turn, the Tower's Rules.
Politically, Irregulars are viewed as beings who have entered the Tower, without being chosen by Headon. Alumik Edrok mentioned that the Tower "opens its gates" to Irregulars, depending on what it needs. According to Yuri Zahard, they're "probably not too welcome" and she assumes Headon doesn't like Irregulars. According to Ship Leesoo, Irregulars have "opened the door themselves of their own will" and their act goes "against the Tower's Laws." The god of guardians calls them "Those who opened the gate themselves" and confirmed they have the power and authority to control shinsu without the need of the Guardian's approval.
Only Irregulars can receive challenges directly from the Guardians. The most important thing about an Irregular, they are "free of all the contracts of the Tower"; most importantly, this means that they are capable of killing Zahard, who has a contract with the Guardians that guarantees that the inhabitants of the Tower can never kill him.
Most known Irregulars have shown exceptional power from the moment they entered the Tower, but it is unknown whether this is a universal property of Irregulars, whether it's something they naturally have as a result of their origin or whether such power is usually just a prerequisite for forcing your way into the Tower in the first place.
Zahard and the Ten Family Heads
Officially, the term Irregular refers to those who have entered the Tower in defiance of the existing system; therefore, Zahard and his companions might not be considered Irregulars, despite entering from the outside. However, in Of the Tower's Weapons, Ashul Edwaru seems to group Zahard among their number, as does Yu Han Sung, indicating that they might be retroactively considered such despite (or perhaps because of) the Regular system not existing in their day. In addition, the god of guardians groups them in this category and refers to them as the "Zahard kids."
The known Irregulars who entered the Tower during Zahard's rule have displayed enormous strengths which eventually became a symbol of fear.
They have a strong relationship with shinsu and have the authority to manipulate it on every Floor from the moment they enter the Tower. Lero-Ro described Baam's display in the Crown Game as "it seemed as if the shinsu attacked on his own volition." Irregulars are also assumed to naturally possess incredible shinsu resistance as evidenced by Baam casually walking in a White Steel Eel nest and not being affected by Lero-Ro's test and Urek's claim that the Opera could only stop him for a fraction of a second. Finally, the most incredible feats with shinsu have been realised by Irregulars: Eurasia proved that just by "accelerating" the shinsu in one area, she could instantly kill 99% of the population living there  Gustang was the first to systematically analyse and classify shinsu and Enryu (who is rumoured to be able to create life from shinsu) showed his shinsu control was superior by killing the 43rd Floor Guardian.
According to Androssi Zahard, she felt she shouldn't fight Rachel and had the feeling she came from "a different place from us." It seems the Princess was unsettled enough to join up with Rachel and even accepted and obeyed Rachel's request to not fight Baam's team. Something similar might also have attracted Khun Aguero Agnis to Baam, as Aguero was one who never trusted others and who never talked to others unless necessary. Yet Aguero thought that Baam was too special to be ordinary and even went out of his way to help him, risking his status. This might also explain Yuri, Black March and Yihwa's instant attraction towards Baam.
According to Alumik Edrok, the Tower only opens its doors for "something it needs," implying that Irregulars are deliberately accepted into the Tower's system to change its status quo in some fashion.
According to Hwa Ryun, Rachel (and, based on context, Baam) are beings that "not even the Guides can foresee."  This could be another way to demonstrate the Irregulars' capacity of violating the Tower's laws and bringing change.
Speculation and Controversies
The current testing system, in which Regulars are selected by Headon, was likely established by Zahard after he conquered the Tower up to the 134th Floor. Since only Irregulars can request to be tested directly by the Guardians, it follows that the only an Irregular (or those travelling with an Irregular) can actually reach the top of the Tower. This implies that the original purpose of the Tower may have been solely to test those now known as Irregulars.
For a long time, there was extensive debate in the fanbase over whether or not Rachel qualified as an Irregular, stemming from the unusual way Headon addressed her in Chapter 76 - the fact that Headon specifically said that she was "not chosen" (an unusual wording, since by the normal definition all Irregulars are unchosen) and debates over just what it meant to "open the door" led many to believe that either Rachel or Baam was not an Irregular. SIU finally confirmed that both were Irregulars in a live chat with fans, but what, if anything, was meant when Headon said she was 'not chosen' (and, by extension, implied that Baam was) remains unknown.
One interpretation of this semantics is that Irregulars are, presumably, deemed by the Tower itself and its Guardians as being "worthy" or possessing the "something" the Tower needs. Essentially they enter and climb the Tower the way the Zahard and the original Family Heads did—opening the door themselves and taking the Guardians' tests. Conversely, Regulars are chosen by systems within the Tower, instated by inhabitants acting on the Tower's behalf via contracts with Guardians (i.e. Headon brings Regulars to the Inner Tower instead of to the doors, other Guardians defer testing duties to test administrators). It is because they bypass these systems that Irregulars are considered "unchosen" by common standards—even if they are "chosen" by the Tower's original standards.
SIU has mentioned the current number of Irregulars in the Tower is secret.
- Enryu (Spear Bearer)
- Rachel (Light Bearer)
- Twenty-Fifth Baam (Wave Controller)
- Urek Mazino (Fisherman)
- Zahard and his Great Warriors
- Ari Han
- Arie Hon (Fisherman)
- Eurasia Blossom (Wave Controller)
- Grace Arlen
- Ha Yurin (Scout, Fisherman)
- Hendo Lok Bloodmadder (Defender)
- Khun Eduan (Spear Bearer, Fisherman, Jeonsulsa)
- Lo Po Bia Family Head (Anima)
- Po Bidau Gustang (Wave Controller)
- Tu Perie Tperie (Light Bearer)
- Yeon Hana (Fisherman, Wave Controller, Hwayeomsa)
- Zahard (Fisherman)
Notes and Trivia
- The Hell Train and its guardians were specifically created by the Gong Bang for the purpose of training Irregulars.