Oh Ruka he thinks you are a sad and crazy young woman and he feels bad for you. He finds much of what Ruka says to be confusing and disjointed, interspersed with moments of inexplicable emotion; he's interpreted this as genuine mental illness of some sort, and that is why he tends to be a bit gentler and less certain with her than he is with others.

So, essentially, with that poor girl - he wants to support her, but isn't sure how to do so; so at the moment, he's mostly staying watchful and trying to get a better sense of who she is and why. But if he sees people being mean to her boy howdy he will step in.