Knights of the Ashen Flame

This person is a member of an organisation that is creating artificial Flame Humans, and the one who killed Rekka Hoshimiya.

Appearance
The person has a very concealing appearance. Their entire face is covered by a white burqa, and the person wears a large white cloak with a cross-insignia on the back resembling that of the Special Fire Brigade. The person also wears a dark jumper with another cross-insignia on it and white cuffs, white gloves, a jagged belt around their waist that holds up their white trousers that have a thick dark line going across the thigh area, and seemingly go all the way down to their feet, covering them.

Abilities
The person is a Third Generation, and awakened the ability to create a bow and arrows made out of flames. Using this, the person can launch fiery arrows from a great distance but also deal a heavy blow; enough to impale a human's chest or sever an arm.

VS. 5th Special Fire Brigade arc
The person appears at the scene of Shinra Kusakabe and Rekka's fight, along with another comrade, where the person stealthily uses their Ignition Ability to impale Rekka through his chest, ultimately killing him, all the while staying hidden from any threats. The person tries to harm the others, albeit unsuccessfully, but manages to cut off Foien Li's arm. After Karim Fulham devises a plan to threaten the opponent, the mystery person decides to leave with the friend, commenting that the "Nativity Flame Festival" has begun throughout Tokyo.