Grail Mercenaries is a term used in the context of the Fate series, particularly in the Fate/Grand Order mobile game. These mercenaries are summoned heroes or figures from various mythologies and histories, who serve as powerful allies in battles. Each mercenary possesses unique abilities and skills, making them valuable assets in quests and challenges. In the game, players can collect and summon these mercenaries through a gacha system, where they can obtain different characters with varying rarities. The Grail refers to the Holy Grail, a central element in the series that grants wishes and powers to those who possess it.