Black ==> How my muse would go about killing your muse (assuming my muse were given cause.)
It’d be interesting to see what could possibly qualify as ‘cause’ for this. Nue is rather fond of Rumia for the shear fact that Rumia is a more classical Youkai and doesn’t try to be something else. But anyway, as with most people Nue wants dead, Nue has three goto options that she uses before ‘getting creative’.
Her preferred option is poison in most cases and Rumia would be no different. But Rumia’s being a Youkai, as well as the nature of her diet would make it difficult. Nue would likely need to find a poison that would work on Rumia, while I have no doubt that such things exist, that’s still a road block. The next issue with poison would be delivery, as Rumia’s diet basically consists of people she’s eating, Nue would have to figure out a way to poison a human without it being obvious and then arrange for Rumia to eat said human.
The second option would be to personally kill Rumia in her sleep. Nue is not one to involve herself in violence and has a strong distaste for it. So if she is going to kill someone personally, she’ll do it as quickly, cleanly and quietly as she possibly can. Being able to look like whatever you damn well please makes stealthy sneaking up on people rather easy.
The third option would be to have someone else do it. This one is incredibly situational. As it would require Nue to either manipulate someone to do it, or call in favours she’s owed (and yes, there are people who owe Nue, scary as that thought is.) The only real reason Nue would use this option is if the reason for killing Rumia was personal and this was an appropriate or ironic response to the reason.
Purple ==> A secret my muse would not want yours to learn.
There’s actually not much major that Nue would be adverse to Rumia learning. Not to say there isn’t any. But Rumia is a Youkai, and not a ‘domesticated’ Youkai either. Which means Nue sees Rumia as more or less a peer (this is over simplifying things a bit, but Nue’s value set regarding other Youkai could fill a few asks itself). So this means most of the stuff that Nue wouldn’t want people to learn wouldn’t bother her if Rumia were to learn it.
The exception to this is the big one. Nue does not want anyone to learn what her limits are, Rumia included. If you’ve ever noticed, Nue is quite willing to discuss what she can do. But as soon as she is asked what she cannot do she get’s evasive fast.