There are multiple differences. Story characters are developed by the game developers to drive the single - player story forward. Their actions and decisions are often scripted to fit the overall plot. Online characters, in contrast, are for the player to shape. You can choose different skills for your online character based on your playstyle, whether it's being a good shooter, a great horse rider, or a skilled hunter. Also, the appearance of an online character can be highly customized, from the face shape to the style of clothing, which is much more flexible compared to the story characters that are set in their appearance and characteristics according to the game's story.
The story characters are designed to follow a set path in the game's main narrative. They have specific personalities and backstories that are part of the overall story arc. On the other hand, online characters are created by the players. You can customize them in various ways, like appearance, clothing, and skills. Online characters are more about your personal experience in the online part of the game, where you can engage in activities like hunting with other players, doing missions together, or competing in showdowns. They don't have the same kind of fixed narrative as the story characters.