Okay, I'm a little surprised this is the question because 'Winter Moon Story' isn't a massively mainstream title—I think you might be talking about Dean Koontz's 'Winter Moon'? If that's it, the cast is pretty tight. The lead is Eduardo Fernandez, a former LAPD cop who moves his family to a remote Montana ranch after a tragedy. He's grappling with grief and then... well, something very not-normal on the property. His wife, Heather, and their young son, Toby, are central too, with Toby's perspective being especially creepy as he senses the unnatural threat.
The other key figure is the rancher who originally owned the place, a man named... Jack? Actually, wait, I'm blanking on his name, but his journal entries detailing the strange happenings are a huge part of the early dread. The antagonist is less a character and more this amorphous, predatory force from the woods, a kind of biological horror that's truly alien. It's a classic Koontz setup: an ordinary family against an incomprehensible evil. The dynamics between Eduardo trying to hold it together, Heather's growing alarm, and Toby's vulnerability really drive the claustrophobia.
What sticks with me is how the isolation of the setting functions almost as a character itself. If you meant a different 'Winter Moon Story,' like maybe a webnovel or something, my whole spiel is useless!