Nimbus the cat's transformation is legendary
"A little TLC can turn a crinkled tissue into a beautiful cloud. Nimbus's transformation was legendary.." - the person who posted the pics to Reddit.
Notice that the before pictures shows Nimbus with 'pink eye' a secondary bacterial infection so typical of stray and abandoned cats. If left it can cause the loss of an eye or eyes. It is cured with antibiotics. See best antibiotics for a cat bite - another story completely.
Not sure of the backstory and history of this white cat. It has to be pretty dire. I am guessing that Nimbus was a rescued kitten or young cat who flowered with plenty of TLC (tender loving care) into a cool-looking white gem. It is always the same reason for the before look and the same reason for the after look. Neglect, abuse or abandonment causes the before look and a ton of genuine love and care results in the after appearance.