Ahhh it's been a while since i've read this series. Forgot how many back-door dealings Rembrandt actually did. IMO I think it's a good bit to include due to, as Tomoe puts it, Makoto being too innocent. His actions are 100% just and well intentioned. What's wrong with saving such pitiful lives? The reveal that Rembrandt is far more than just a "shady guy" puts into perspective how naive our dear protagonist may be, or not be. It definitely should get Makoto to start second guessing who he interacts with... UNLESS he doesn't particularly care. It's hinted a few times but Makoto is a bit sociopathic. He cares deeply for the ones he loves, and he has shown empathy. But as expressed in a previous chapter, despite being born in a relatively peaceful home and city where death isn't as common as a fantasy world, he doesn't bat an eye at corpses or have any particular qualms at the lost "enemy" lives. While it's common for isekai protagonists to not really give two shits about these sort of qualms, it's nice to see a series acknowledge this abnormality.
Tomoe hiding Rembrandt's secrets though... I wonder if that was a good idea. Perhaps, it'll serve as a future breakpoint in Makoto's trust in others. I see it as a mother covering her child's eyes. She doesn't want Makoto to get hurt.