Okay, so this is one of those weird, deep-cut internet lore things. The main story is basically Jack's origin as this supernaturally unlucky fox dude. He was originally a human boy who got cursed after making a deal with the demon Cain from 'Zoophobia' to save his sick sister, Faye. The curse means he constantly brings disaster everywhere he goes, and he's immortal, so he's just been wandering for centuries, miserable and alone.
You follow his past, his endless attempts to break the curse which always backfire spectacularly, and his eventual arrival at the Safe Haven Zoo where the main 'Zoophobia' webcomic takes place. It's less a straight A-to-B plot and more a tragic character study spliced with dark humor—every time Jack tries to do something good, the universe literally collapses on him. The art style shift from the cute main comic to this grittier, more detailed look for Jack's story is a huge part of the vibe.