Yeah, I know, it's a little odd and not something I'd normally do, but I think it's justified here. One, that's just how the story unfolded when it came to me, and I usually don't change too much of the initial inspiration. Second, it's two very different contexts (the first being Muna's choice, the other just part of the test itself). And finally, I wanted to emphasize the fact that it's a girl being initiated into a group of dudes, the feminine fourth element being introduced into a predominately masculine trinity, and one way to contrast the masculine and feminine is through sexual tension (in this case, fairly mild). There's some Jungian archetypal stuff going on under the hood of the narrative, if one decides to dig deep enough.
In other words, I thought it out before I decided to do it, it's not just mindless fan-service.