I'll try to give you the short version of the story without the dialogues. Swain's mother was like Rakan and Xayah, half bird half human and his father was a Noxian that rescued her and fell in love but when Swain was born he had some type of problem to his leg and also bird characteristics due to his parents which later drove him into hating them. His mother tried to help him through this by gifting him her companion bird that would enchanche his powers but although he accepted it he still despised her, his father was suspicious and worried because he foreseed his son's betrayal. After rising into the military ranks of Noxus due to his master tactician skills while being constantly harassed for his ''corrupted blood'' he became more fanatic against non-human creatures as well as the humans who harassed him and at the end he felt that his parents cursed him. He finally ordered a purge of the city from all the ''corrupted non-humans'' but some people still continued to have a bad opinion for him due to being one of them himself. That day he personally went to his house and once he entered it his father and mother both knew that their son was now an enemy and that they wouldn't be able to convince him, but his mother was more surprised about her companion bird not obeying her and being on Swain's side. She would never attack her own son, his father tried to protect her but only made things worse, the house was surrounded by dark flames, Noxians and Swain, his parents hugged each other smiling and closed their eyes in their final moments, the moment after Swain's new powers appeared in a circle surrounding them and everything turned dark. Swain didn't drop a tear at all. After the city's purge was completed Swain was titled as the liberator of Noxus and in addition to his tyranic actions against those who despised him, finally everyone came to aknowledge him as their leader. This is how Swain the Master Tactician came to exist (or not).