Type-Moon, but Assassin's Creed

Lin Qiwen, 19, is a Templar Knight who defected to an organization of assassins. All she wants is to slack off, but the stolen Holy Grail chooses her, making her the only Master capable of commanding Heroic Spirits! Right now, "Heroic Spirits appearing out of nowhere without being summoned" are cropping up all over the world. To keep the world from being destroyed, she has no choice but to team up with a wealthy Japanese heiress, whose true identity turns out to be... This isn't a Holy Grail War! Next, she walks the line between the Assassins and the Templars, making contracts with Heroic Spirits once famous throughout history, making them blush, and... Wait, I'm mixing things up! It's like collecting Pokemon!