Well I can already see where this is heading... this is nearly exactly like that movie with Ethan Hawke, Predestination, I mean the title of the game is Paradox which was basically the exact point of the other story, a self-fulfilling paradoxical prophecy. So my assumption is the MC is his own father via Tabitha, he was sent back in time to stop the Great Quake only for him to inevitably be the one to cause it, probably in retaliation of them killing or trying to kill Tabitha, I also assume the person that stopped Vanya from killing him is likely his own future self that created the agency to basically satisfy the loop that lead to his birth, or perhaps Tabitha herself, keeping the cycle of the Paradox going.