Amadeus

What The Wings of Amadeus are.
The Wings of Amadeus is a secret organisation that intents on taking over The Holy Kingdom of Aria and to eliminate all demons.

Maria is the daughter of the Leader, who has passed away.

To ensure that they can take over The Holy Kingdom of Aria, they use skills to eliminate other potential queens and to ensure that Maria becomes queen.

Once they've done that, they organise military power and start campaigns against demons.

The reason for the termination is The Human-Demon War.

The history of The Wings of Amadeus.
Amadeus used to be an Adventurer Mercenary Group that got paid by The Holy Kingdom of Aria to combat the demons. In the first Human-Demon War, the Leader and multiple group members got killed which made them dislike and even hate Demons.

Maria was chosen to be the new leader as she is the Leaders Daughter. Maria has reformed Amadeus to be a Team that protect and serve her: The Wings of Amadeus.

The Wings of Amadeus protect and help her to become the queen with the goal to punish the Demons.

The Feathers of The Wings of Amadeus.
After Maria became the queen, The Wings of Amadeus have formed the The Feathers of The Wings of Amadeus (TFTWA). They serve as the new millitary and guards of The Holy Kingdom of Aria.

They punish those are against Maria and Amadeus and have banned Demons from entering the country.

Maria and Amadeus were the cause of The Second Human-Demon War.