A pastel cat is something you call an amazing, lighthearted, soft person. They remind you of a cat, soft, fluffy, and cuddly, but also a nice light calm pastel color.
A genre of music containing bands whose t-shirts and other related artwork are characterized by bright, loud colors (pastel) and nonsensical designs. Usually worn by some skinny douche who thinks he's "brutal" or "hardcore" because of listening to said band(s). Generally just awful music but not always.
Example of bands that could be considered "Pastel-core" are Asking Alexandria, Suicide Silence, A Day to Remember, August Burns Red, etc.
PastelRay is an animation youtuber. She’s pretty neat and, what I examined as, carefree. She also has a girlfriend named Kayra and their ship name is KayRay.
Person: Pastel Ray posted a new video!
Person 2: Really? We gotta watch is real fast!