As in, Princess Zelda in disguise.
Sheik is/was an unrepentant badass both as Sheik and as Zelda. And it fits the entire theme of the Vigilante almost to a tee.
Fighting games may not be the best example in the world to base a TRPG's designs off of, but I feel like this is what the class should be aiming for:
A quick-changing character with two "modes" that accomplish radically different goals and allows the player to switch between the two when needed.
Obviously in Smash Bros., Zelda & Sheik are both stat'ed out to be combat-focused types, with Zelda being focused on long-range attacks and higher defense while Sheik is all about melee combat and speed/agility. But the fact stands that the design is very solid, interesting, and allows for players to play as they choose.
There are some players who never leave the Zelda guise, there are others who use Sheik exclusively. And, obviously, you have players who switch between the two constantly.
2 thematically-different classes can exist in one whole class without breaking the game; they just have to have the right balance, both with each other and among other Classes.