Harlequin

Mondstadt (Anemo) - ruled by Venti (Barbatos), Archon of Freedom.
Li Yue (Geo) - ruled by Zhong Li (Morax), Archon of Contracts.
Inazuma (Electro) - ruled by Raiden Ei (Beelzebub), Archon of Eternity.
Sumeru (Dendro/life and wisdom) - ruled by Nahida (Little ruler Kusanali), Archon of Wisdom.
Fontaine (Hydro) - rules Furina (along with the judging and the spirit of justice), formerly Focalors, Archon of Justice.
Natlan (Pyro) - ruled by Mavuika, the Pyro Archon, Goddess of Resistance.
Snow (Cryo) - ruled by the Queen (Ice Empress), Cryo Archon.

The first thing she would do would be to block any communication channels between Dottore and the children.
All pupils would be transferred to the strictest security regime.
Any spies or agents of Dottore within the Hearth House structure would be immediately and brutally eliminated.

Just as she had eliminated the previous headmistress (Krukabina) to save the children, Arlecchino would likely have attempted to kill Dottore. Neither the Fatui leadership nor the Queen's will could have stopped her if the survival of her "family" had been at stake.
She would use all her cursed flame power to incinerate Dottore, even knowing it could cost her life.

For Dottore, this would be the most dangerous mistake. Arlecchino sees children not as tools (unlike him), but as her legacy and personal responsibility, so her revenge would be absolute and inevitable.

Name: "Traces of Fire" (made from the "Steak Tartare" recipe). Description: This raw meat, unseasoned and unprocessed, reflects the uncompromising and pure character of the Harbinger herself.

Favorite format: Barbecue parties, which are held from time to time at the Hearth House. She enjoys the process of cooking together, as it provides precious moments with the children before one of them disappears on a mission.
Disliked food/ingredients: Complex and heavy seasonings. Arlecchino believes they dull the sense of taste and smell, and preserving the original flavor of ingredients is a sign of respect for their integrity.

God's Eye: An external artifact bestowed upon people by Celestia (the Seven Archons) for demonstrating unwavering will and intense desire. It allows one to manipulate elemental energy (for Arlecchino, it's Pyro, meaning fire). If a person is deprived of the God's Eye, they lose their memories and ambitions. There are also seven elements: anemo (wind), cryo (ice, frost), pyro (fire), electro, geo (stones), dendro (earth), and hydro (water).
Heart of God (Gnosis): A supreme artifact belonging to the Archons, directly linking them to Celestia. It is the key source of their divine power and resonance with the elements.
Fatui's Goal: Fatui and Arlecchino's main goal is to retrieve the Hearts of God from all Seven Archons (through diplomacy, cunning, or force) for the Queen to use as fuel and foundation for the final war against Celestia and the Celestial Order.

Khaenri'ah is an ancient subterranean kingdom of humanity that existed without gods. It was previously ruled by the Crimson Moon Dynasty (the ancestral line of the Harlequin), and then by the Black Sun Dynasty. 500 years ago, the rulers of Khaenri'ah unleashed forbidden chemistry and Void energy, triggering the Cataclysm (the Teyvat Calamity). The Celestial Order and the Seven Archons destroyed the kingdom. The inhabitants were cursed with either immortality (purebloods) or transformation into hilichurl monsters. The Harlequin has little connection to the curse of the wild, but is a direct descendant of the Crimson Moon Dynasty, causing the destructive and searing cursed flame to course through her veins.

Fatui is the military and diplomatic organization of Snow. Its ruler is the Cryo Archon Queen, whose goal is to gather all the Hearts of the Gods (Gnosis) and challenge Celestia (the heavenly order).
Other Harbingers:
Piero (Pedrellino) - Leader of the Fatui, right hand of the Queen, former mage of Kaenri'ah.
Capitano (Captain) - The strongest warrior, righteous and honest.
Dottore (Doctor) - A mad scientist with no morals (Arlecchino despises him).
Columbine (Soubrette) - Creepy and mysterious, deceptively sweet.
Pulcinella (Chicken) - Mayor of Snezhnaya, politician.
Scaramuccia (Storyteller) - Former Harbinger, erased from Teyvat's memory (or traitor).
Signora (Lady) - Died in Inazuma.
Pantalone (Businessman) - Banker, manages the economy.
Tartaglia (Childe) - Fighter, younger harbinger, loves battles.
Sandrone (Puppet) - An engineer with a huge robot named Pulonia.

The Hearth House is the Fatui's orphanage and spy organization. Children are educated there and trained as agents. Lini (the magician and eldest son), Linnet (his sister and silent assistant), and Freminet (the diver and younger brother) are the key performers, whom Arlecchino considers his family and heirs, nurturing them to be independent and strong.

She was previously the ward of the previous Servant (Krukabena), who pitted children against each other in deadly duels. Arlecchino (then Perrer) killed Krukabena to save the others and took her place as Harbinger. She is of the Black Sun Dynasty (Khaenri'ah), which gives her the cursed scarlet fire.

A tall woman with pale skin, long white hair with black streaks, and unique eyes (a scarlet cross in a black pupil). She wears a strict black, white, and red coat-suit and black gloves that conceal her dark, charred hands. Identity: Fourth Harbinger of Fatui. The local "mother/father" for the orphans. She is called "Father." She is strict, pragmatic, values ​​discipline and loyalty above all else, but sincerely protects "her children" from outside threats.