Posted on 18 February 20 at 21:34
What shadow said. If it's available as a difficulty from the beginning, it's considered main storyline. Sure you can not get it by playing on a lower difficulty, but it's there from the beginning. Selecting it will let you get it through natural progression.
If it's unlocked once you beat the other game, or by other methods, then it's not.
Feel free to submit flags for this game, whether to correct us, or to debate on some. This game was (for the most part) flagged when guides weren't available. So some might be incorrect.