Going back to the Kirby comparisons from a couple of pages ago, it's interesting to think about why Nintendo thought, or maybe knew, Kirby - and to some extent his predecessor Lolo - would be a successful franchise internationally, to the point where they didn't even bother to hide his cuteness on the box art, and why they didn't put that same faith in Panel de Pon.
According to an article on the subject, Nintendo of America works together with their Japanese branch and Hal Laboratory so they have a better idea of what sells the game best in different regions. In Japan, of course, the games are popular because the main character is an adorable pink marshmallow creature. Internationally, the games are popular because the main character is an adorable pink marshmallow creature who also kicks major amounts of ass. This is the reason for that period of time from around 2003-2011 when Kirby had a serious facial expression on international, or at least North American, box arts.
Looking back, there was nothing keeping them from doing the same thing with the fairies, and the box art for Tetris Attack shows no mascot characters either way. There's plenty of official artwork with the fairies being "hardcore" - just look at my avatar. There's nothing keeping them from doing it now, in fact. If they're still worried a game with Lip on the front cover will flop just because she's a cute girl (certainly not a rational fear anymore with the recent popularity of games, indie and otherwise, starring cute female protagonists), why not just show her and a few of her friends fighting a monster?