The Story of Kassadin
Kassadin was a human guide and scout who spent years navigating the edges of Shurima's magical dead zones — places where Void energy had begun to corrupt the landscape. He was practical, grounded, and good at surviving in hostile territory, which made him valuable to the scholars and mages who hired him to take them into places their books described but their bodies weren't equipped for. His daughter Kai'Sa was with him when a Void incursion consumed her village.
He searched for her for years. He found evidence she had survived — had adapted, had become something that the Void had not entirely claimed — and in pursuing this evidence he went deeper into Void-touched regions than any human had survived before. He didn't survive entirely intact. He was exposed to Void energies that would have killed a less determined person, and he survived by equipping himself with Void-touched artifacts and technology that let him resist the corruption even as it changed him. He is not fully human anymore.
His mission now is the Void itself. He fights its incursions not as a soldier following orders but as someone who has looked into what the Void does to people he loves and decided to dedicate whatever is left of himself to preventing it from doing more. He still doesn't know exactly what his daughter became. He hopes, when he finds her, that she is still in there.