I was going to suggest this could be where the Seraphim, most wanted murderer could show up?

Also if Lucifer is condemned to eternal torment, would it not be easier for Michael or the seraphim to target and use Varia against him? Like threaten to make her a fallen or condemn her to eternal damnation?

You can still have him struggle against his own self in the meantime - is the end goal to have his angel side win or have his darkness forever consume him?