[He's a hundred years old at least. He lost track ages ago. His situation isn't exactly the same as a Grisha's, though. From what Nikolai's saying, he's a lot closer to whatever's going on with him.]

...Well, not exactly, but...

[The similarities are uncanny. He keeps watching Nikolai, noting the shift in how he holds himself, the crumpling of his brave front. Brook's not the empathetic sort, but he's been around for a long time. He can pick up some cues.]

Look. You don't want people to know about you, right? Let's go somewhere else, where the light isn't doing... [He waves vaguely at Nikolai and the room in general.] That. There's a little park or something not far from where the train stops. We can talk and walk.

[So he turns and leads the way out of the green room, too. As he crosses through the installation's main lobby, heading for its exit, he even makes good on the offer to talk.]

My "ancient evil being" didn't die. He can't. But he did put a demon in my body so I can do my job for him.

[Shrug.]

I agreed to it, though, so it's fair. And he made this body in the first place, anyway. In the end, I guess he can do what he wants with it. I wouldn't be able to stop him now, and I definitely couldn't then.