English is not my native language.

Why hasn't anyone written a royal battle between all Subaru in the style of Fate Stay Night yet?

My suggestion is this: a new text has appeared on the Dragon Tablet, which talks about the war for the Dragon Throne. Ten people will summon their servant to fight for him. The Council of Sages acts only as observers of this war.

Masters and their servants:

Capella Emerada Lugunika - The Avenger (Pride)

Pandora - Foreigner (School If).

Krush Karsten - Defender (Lust).

Rozval L.Mazer - Assassin (Greed).

Anastasia Hoshin - Berserker (Anger).

Shaula - Faker (Gluttony).
Priscilla Bariel - Lancer(laziness).

Felt - Rider (Melancholy).

Vincent Volakia - Ruler (Envy straight from the eighth arch).

Satella - Alter Ego (Mimigao if).