I heard that Tadashi actually came up with the idea of making 2 into two games about halfway through writing Innocent Sin. Still, while many people use this claim to say that it was intended to only be Innocent Sin at the start (those are mostly people who didn't like EP's ending compared to IS's ), pretty sure rewrites were made to the IS part to solidify the games as two halves of the same whole because there are way to many things in IS foreshadowing EP to not make it feel like this is intentional from a narrative standpoint and not just "hey let's just make two games and get twice as much cash!"