PSA: Some Muses Won't Open Up To Yours
I've kind of touched on this before in noting that while there are plenty of PSAs in the RPC telling you to let villain muses be villains, or to respect powerful muses, I've never seen one besides my own telling you to remember that not every interaction will be deeply meaningful...
... But I think that advisory can be extended further still by also saying there are muses that aren't likely to or simply will not open up to your muse(s) for various reasons.
This is most often true for muses who, for whatever reason, are part of 'the elite' of their original settings; individuals who have had to take on roles of duty or authority and who at some stage may have essentially put on a mask to hide their true nature. That mask might be hostile, stoic, playful, flirtatious, or anything in between. They might even have many masks befitting whatever situation. And whatever mask(s) they have might not ever come off.
For anime muses in particular, you'd better believe they were originally designed by people with a deeply ingrained knowledge and understanding of giri versus ninjō (duty/obligation versus emotion/compassion) as the tension of this dichotomy is a core theme of Japanese culture. Whether you RP them with this consideration in mind is your own business and choice, but if your muse strongly represents that tension, you're probably aware of it to some extent even if you've never heard those terms before.
Muses like this may drop their masks around your muse(s), but they may also not. Whether they do or not is really all about how the two muses fit together. But you cannot a priori expect every muse to open up to yours. If a muse doesn't, it's more than likely nothing personal. And if that muse always seems poised, composed, on the ball, or whatever else, that does not necessarily mean that muse is being roleplayed as flawless, superior, or whatever else—making your muse and even you as a mun feel that way is probably exactly the point of the mask(s) that muse wears.
You should not expect openness or vulnerability to come easily or early in interactions with such muses. In fact, you should not expect it to ever come at all. And if it doesn't, that doesn't mean that muse hates yours, or the mun hates your muse(s), or the mun hates you, or the muse is poorly written. It only means that muse is hard to reach and the mun has decided to be true to that aspect of them.
Calibrate your expectations accordingly.
