An organization of Denizens who moved into the human world several millennia ago under the Grand Master and the God of Creation, the Sairei no Hebi (「祭礼の蛇」, "Snake of the Festival"). Since the Flame Hazes defeated him and sealed him in the Abyss between the worlds, it has been led by three powerful figures known collectively as the Trinity and became an organization to support Denizens. Their goal is to accomplish the Grand Order, with a Power of Unrestraint called the "Psalm of Grand Order" and the Midnight Lost Child being necessary for their plans. Its subordinates are mainly classified into three roles; Wanderers, Jaegers, and Heralds.
- Hecate / Itadaki no Kura Hekatē (「頂の座」ヘカテー, "Master Throne") ("Supreme Throne" in the English anime) (Crimson Lord)
- Voiced by: Mamiko Noto (Japanese); Brenna O'Brien (Season 1), Lindsay Seidel (Seasons 2-3) (English)
- A member of the Trinity known as the "Priestess", who Bel Peol describes as having an "eternal existence". She controls the movements of Serei-den, Bal Masqué's base, and wields a Treasure Tool called Trigon, which resembles a staff. Her position is important to Bal Masqué's plans, as she can send the Midnight Lost Child's power to everything in Seireiden. She has taken up the habit of prayer, though she has no one to pray to, often lamenting that she is 'empty'. The light novels imply that she is praying to the Snake and depict her as a leader that even Bal Masqué fears. She is skilled at using Aster, a Power of Unrestraint which shoots energy beams, and has a flute that can summon dragons made of blue flame, which she plays when announcing the end of Serei-den's anchoring.
- In the anime, Hecate synchronizes with Yuji, allowing her to draw on his sense of self to fill the void within her. The true nature of this synchronization is revealed at midnight, when the Midnight Lost Child attempts to restore Yuji's Power of Existence. As a result of the synchronization, it begins to emit an infinite amount of power in an attempt to fill Hecate's capacity. She considers the feelings that she gets from synchronizing with others are hers and no longer from their owners, much like a Torch being the remainder of their original human self. However, Yuji tells her that the feelings, memories and sense of self are his and that she is just as empty as she was before synchronizing and cannot possibly fill her sense of self by drawing it from others. Because of this revelation, she is forced to confront the emptiness within her, and her despair causes her to lose control of the synchronization, Serei-den, and herself, releasing the Power of Existence she stored while synchronized with Yuji and requiring Sydonay to save her. Later, during Xanadu's creation, Hecate becomes the sacrifice needed for its creation and reunites with Sydonay in the afterlife.
- Sydonay / Senpen Shudonai (「千変」シュドナイ, "Metamorphosis") (Crimson Lord)
- Voiced by: Kenta Miyake (Japanese); Eli Gabay (Season 1), Jason Douglas (Seasons 2-3) (English)
- A member of the Trinity known as the "General", who remained outside the organization because he sought the freedom to do as he pleased, but assumed his current position after finding the Midnight Lost Child. It is implied that he and Margery fought in the past, as Sydonay describes their current battles as a reunion. He has shape-shifting abilities and, unlike other Denizens, can transform into various chimeras without using spells. He also wields a Treasure Tool called the "Shintetu Nyoi" (神鉄如意, "The Divine Metal at Will"), which resembles a spear. With this weapon in hand, he leads an army of Denizens and Lords, destroying major Outlaws throughout Europe and China. He cares deeply for Hecate and comes to her aid even in the midst of battle, as when he abandons his fight with Margery. He chooses to stay behind when the gate to Xanadu opens, reuniting with Hecate in the afterlife after Margery kills him.
- Bel Peol / Gyakuri no Saisha Beru Peoru (「逆理の裁者」ベルペオル, "Arbiter of Reverse Reasoning") (Crimson Lord)
- Voiced by: Sayaka Ohara (Japanese); Paula Lindbjerg (Season 1), Caitlin Glass (Seasons 2-3) (English)
- A member of the Trinity known as the "Strategist", who is willing to manipulate her subordinates and send them to their deaths, but is also capable in battle. Unlike most Denizens, who live their lives freely, Bel Peol accepts the obstacles that stand in the way of her plans, feeling that overcoming them is what makes life interesting..
- Fecor / Rantei Fekorū (「嵐蹄」フェコルー, "Ungula Tarantula") (Crimson Lord)
- Voiced by: Yasuhiro Mamiya (Japanese); Cris George (English)
- A Lord who usually acts as a guide for Seireiden and greets Denizens and Lords at the gate, but is secretly Bel Peol's right-hand man, being in charge of Seireiden's defense. Despite his appearance and demeanor, he is powerful and can use a Power of Unrestraint called Magnesia, which creates storm of heavy particles that he can manipulate and use for both offense and defense. He later appears in Misaki City as Hecate's bodyguard to protect her from the Flame Hazes. He is killed by Tenmoku Ikko while guarding Bal Masque and the Dimensional Gate.
- Sabrac / Kaijin Saburaku (壊刃」サブラク, "Destructive Blade") (Crimson Lord)
- Voiced by: Takaya Kuroda (Japanese); Brad Jackson (English)
- A Lord who is an assassin working for hire and has won many battles against the Flame Hazes, but only chooses targets he finds interesting. He collects and wields bladed weapons, and his Power of Unrestraint, Stigma, causes the wounds he inflicts to increase in severity over time. Sabrac has a large stature, yet possesses the senses of a human, and hides his body by blending into his surroundings, allowing him to attack undetected. The humanoid form that he can create to attack is nearly invulnerable because it is created from a small part of his body. After Bal Masqué hires him, he puts a part of "Psalm of Grand Order" into the Midnight Lost Child. Bel Peol later hires him and he attacks Misaki City, injuring the Flame Hazes there and putting another part of the "Psalm" into Yuji. However, his arrogance allows Wilhelmina to cure the wounds Stigma inflicted and Yuji deduces his true nature, defeating him by severing the connection between his humanoid part and his true body. Despite this defeat, he escapes using the power of the Gordian Knot. He is ultimately destroyed after falling into the Abyss, having lost the will to fight upon seeing the Snake of the Festival's true form and refusing Bel Peol's aid.
- Dantalion / Tantankyūkyū Dantarion (「探耽求究」ダンタリオン, "Seeking Researcher") (Crimson Lord)
- Voiced by: Nobuo Tobita (Japanese); Michael Dobson (Season 1), Barry Yandell (Seasons 2-3) (English)
- A mad scientist who is willing to conduct research on his fellow Denizens, being responsible for experiments that created some of the powerful Flame Hazes, and will work with anyone in order to achieve his goals. He is also notorious for conducting experiments for the sake of conducting experiments, which annoys others. Bel Peol does not like or trust him and Sydonay hates him, but Hecate is close to him. Near the end of the Second Great War, Sale threw one of Dantalion's own creations, a mass-produced robot primed to explode, under the tower where Xanadu's creation was taking place. Dantalion believed he would be able to escape through an escape route, but was unable to escape because Para had accidentally disabled it. The robot then exploded, killing Dantalion and Domino in the blast.
- Vine / Ryūgan Wine (「琉眼」ウィネ, "Glazed Eyes") (Crimson Denizen)
- Voiced by: Tatsuhisa Suzuki (Japanese); Peter New (English)
- A Jaeger and a subordinate of Bel Peol. He brings the Gordian Knot, which can activate a large-scale destructive Power of Unrestraint, to the Palace of Heaven's Road to stop the exaltation of the new Flame-Haired Blazing-Eyed Hunter.
- Orgon / Senseirei Orugon (「千征令」オルゴン, "Commander of Thousand Conquests") (Crimson Lord)
- Voiced by: Atsushi Ono (Japanese); Scott McNeil (English)
- A Wanderer and a subordinate of Bel Peol. He is sent on a mission to The Palace of Heaven's Road, where he dies after facing his old rival - Rainbow Wings, Merihim/Shiro.
- Zarovee / Shūsan no Tei Zarōbi (「聚散の丁」ザロービ, "Collation Flux") (Crimson Denizen)
- Voiced by: Yukihiro Misono (Japanese); R Bruce Elliott (English)
- A Jaeger with the ability to split into five duplicates, each wearing scarves in red, blue, yellow, green, and pink, but are weaker than a Torch or Flame Haze. He kidnaps Yuji by threatening to consume the citizens of Misaki City in order to lure the Flame Hazes into a trap. However, Yuji ambushes them and destroys one of the duplicates with a fireball and places the hostages under a Seal. The other duplicates are soon killed by Yuji wielding Blutsauger.
- Bifrons / Kōgōga Bifuronsu (「吼号呀」ビフロンス, "Howling Fang") (Crimson Denizen)
- Voiced by: Hiroki Yasumoto (Japanese); Cole Brown (English)
- A Wanderer who usually works with Zarovee and uses a Treasure Tool that grants him stealth in exchange for speed and mobility. He is skilled in fighting from a long distance with projectiles shot from his cannon-like body. When Yuji prevents their scheme, Bifrons fires upon Shana, but dies after being injured in the ensuing explosion and after Sabrac forces him to shoot a cannonball with full power.