In a previous chapter, I wrote about how Rintaro didn't so much ask Subaru for permission to continue meeting Kaoruko as he was asking her how he could make her feel comfortable with it. And by that, he gained an ally. Here she shows just how much of an ally she is.
Late to the party, but I really loved that he reached out to her to help w/ the situation b/c he trusted that she would, knew he couldn't, and knew that Kouroko would try to handle this on her own but would appreciate (rather than be hurt) that Subaru stepped in to help.