Like Nicolai, I have this problem where it's really damn hard to pick out a canon point for Janus. Thankfully, unlike Nicolai, this isn't because of the game's writing sucking or whatever - it's just how his character arc played out. Which made sense, even if it ended too soon! He ends up being the Prophets' (aka the OTHER midbosses) "sacrifice" by ... basically being turned into a demon partway through the game and then given a Dark Spear that gave him a ton of power. But this also enabled the Prophets to awaken this old, dead, REALLY FREAKING POWERFUL demon named Siegfried at Janus' expense. Janus powertrips, gets totally high off of it, nearly KILLS THE PROPHETS and then gets backstabbed (... literally) by Siegfried.
Anyway, Janus is post-chapter two of the game. In other words, he died, he knows he died, and he knows he got played hardcore and was basically screwed around with like mad in the second chapter. This is the most logical place to take him from! Plus, there's a lot to play with, and he gets some interesting development. At the same time, there's also problems because lol demon lol dark spear lol dead. You know, that sort of thing. As a demon, he kind of ... needs the Dark Spear. But given canon and whatnot, er. Yeahhhh.
ERGO. I will not be playing the demon. He died, he is human and therefore is not much of a godmoding twink, and that will make him a little more playable than it would otherwise since the Dark Spear stirs one's "worst impulses." It might be fun for something later on! But HANDWAVE HANDWAVE, the ~magic of camp~, it's really not as fun to have an overpowered character ALL THE TIME and it's not exactly him, etc.
Questions/comments/concerns can go here! I'm definitely playing fast and loose with this, yes, and I'd hate to step on any toes.