Is my story idea original enough?

Focus less on whether the "idea" is original and more on how you execute the characters. Using the seven deadly sins as a framework is a common trope, so the plot beats themselves won't be what makes your story stand out. Instead, you should focus on the irony of your characters' situations. Try to avoid making the sins too literal. If the "Greed" character is just a rich person who wants more money, it'll feel predictable. Instead, explore how that sin manifests in a surprising way, like someone who hoards affection or knowledge. The more you subvert the reader's expectations of those archetypes, the more original the story will feel. Since your plot relies on a big twist—the characters unknowingly helping the villain—you need to plant subtle clues early on. If the reveal comes out of nowhere, it might feel like a cheat. Make sure the "rewards" the villain gives them have a hidden cost that hints at his true nature. Your next step should be mapping out the specific motivations for each of the seven people. If they all have distinct, conflicting goals, their internal friction will drive the plot more than the overarching mystery of destiny. This approach shifts the focus from a familiar concept to a unique human drama.