Okay, I had a darker thought. This was probably not Yukinobu Tatsu’s intention, but Rin’s new power is starting to feel like commentary on the idol/entertainment industry.
So Rin’s whole gimmick is that she’s a pop idol. When she first gets her powers, she is given this really tacky, sexualized costume that she hates. This was her main costume for several chapters until her idol power increased, which unlocked her ability to change/upgrade outfits. So now Rin’s new costume is this respectable black suit that is far less sexualized than the original one. Also, it’s black because, presumably, it represents Rin’s love of dark romance (aka vampires).
You see where I’m getting at? When Rin was first “starting out” as a pop idol superhero, her costume was super tacky and sexualized. The original costume wasn’t her idea, the idea came from her manager Mai. Then when she got more “idol power” (goodwill, fandom, negotiating power, wealth, notoriety, etc), she was able to change her costume into something she actually likes and is far more respectable than the original outfit. Because with more power, you get more freedom.


















