Gate

In Ability-derived life-forms, the Gate (門,) refers to a seal that binds their Singularity intact inside their body. Opening one's Gate even for a brief moment or merely slightly can result to a catastrophic unleashing of a bestial Singularity in the physical world.

Description
Each artificial Ability is made with a seal command that serves as their unique authentication code to open their Gate. In the case of gravity-type Abilities, opening it results in an Ability-phase expansion together with -esque high-energy rays that exponentially increase, involving space itself. The Gate can also be opened either according to the user's own accord or forcibly by another party.

Paul Verlaine
Verlaine can open his own Gate and others' upon contact. He is also able to open it subtly, indicating how he can adjust how much it can be opened. When his Gate is opened, Verlaine succumbs to Brutalization, during which he loses consciousness and unleashes Demonic Beast Guivre's power. Verlaine can open his own Gate by reciting his control incantation:

"Your hate, your set torpors, your weaknesses, your spite, All the brutalities you suffered long ago, You return to us, all without evil, O Night, In an excess of blood that every month will flow."

N was able to remotely open Verlaine's Gate by firing powder made of a rainbow-colored Ability metal. This method was written in The Secret of the Gentle Forest authored by Verlaine's creator, Pan.

Verlaine devised a way to automatically close his Gate, which is to have Chūya Nakahara physically touch him as a result of the command sequence he inputted in the boy.

Chūya Nakahara
Highly implied to be a persona model, Chūya possesses a Gate that can be opened using a control incantation to initialize his command sequence. When his Gate is opened, Chūya succumbs to Corruption and taps into Arahabaki's power.

During Verlaine's and Arthur Rimbaud's mission in raiding a Japanese military research facility, Rimbaud unwittingly absorbed Arahabaki's seal in Chūya rather than Arahabaki itself. As a result, the beast appeared and reduced the surrounding area in black flames, thereby creating the crater shape of Suribachi City. Chūya later experienced his Gate being opened by Verlaine slightly for 0.3 seconds, which caused gravity around him to go haywire and level an entire city block. Eventually, Chūya learned the couplet incantation to open his Gate on his own will:

"O grantors of dark disgrace, do not wake me again."

As the one who designed him, N also knew about the control incantation and once tortured Chūya to willingly release Arahabaki. N was then capable of inputting his character set and overriding Chūya's personality with a new one once they deleted it, albeit ultimately failing to do so.

Thus far, the only way to stop Chūya's Corruption and thereby close his Gate is Osamu Dazai's Ability, No Longer Human, which nullifies his Ability upon physical contact.