Shirou Emiya is the chief protagonist in Fate/stay night who serves as the Master of Saber during the Fifth Holy Grail War. In Puzzle and Dragons, he’s one of the strongest leaders in the business.
Saber is a Knight of the Sword summoned for the Holy Grail War, and this gives her all of the right skills to take on a leadership role in Puzzle and Dragons. As she can use any Attribute on her team, Saber is about as versatile as they come.
But these three are not the only characters joining Puzzle and Dragons with this collab. You should also keep an eye out for Rin Tohsaka, Illyasviel von Einzbern, Shinji Matou, Servant, Archer to name just a few of the exciting additions to the game.