[ Nikolai is trying to make the various pieces line up. Scarlet is Brook's friend, another Reaper who'd struggled with her demon and who Brook had tried to help. And Satan was the entity that had made Brook's body and given him a demon so he could be a Reaper and... do whatever it is Reapers do that Brook didn't want to talk about.

He's confused for a moment why Brook would've needed to tell Satan he was a Reaper in the first place, when it clicks that the pronouns don't match, anyway. There's a lightbulb moment, and he asks: ]

Wait, so this is a different boss than the one that gave you your demon?

[ There are too many pieces of the puzzle missing for Nikolai to really see the picture, but he can at least grasp the frame of it. Brook had kept his role as a Reaper a secret and worn a mask to do it. He'd trusted a woman with that information, and she'd betrayed Brook's secret, and things had gone badly. ]

Well, that was a cruel thing for her to do if you ask me.

[ A hint of a sneer creeps into Nikolai's voice; he has a particular distaste for back-stabbers, and none moreso than people in power who use their position to treat those they ought to be responsible for poorly. ]

I'll do the same, of course. No one will even hear the word Reaper, from me.

[ He mimes locking his lips with a key and tossing it over his shoulder. The gesture itself is comic, but the look in his eyes is deadly serious. ]