I've always found, especially with combat characters, that a dynamic is quintessential. That is to say, there needs to be a "rhyme and rhythm" to how they do things, both on and off the battlefield, a synergy of who they are in action and who they are in person. RWBY is an excellent example of this, as most of the weapons also express a lot about their wielders. Weiss, for example, is often extremely rigid in her thinking and very to-the-point, even though this behavior has come back around to bite her in the past -- a rapier, which is to say a non-curved, pointed, double-edged blade which, while graceful, is also extremely direct in function, is the perfect embodiment of her personality. Blake is a versatile and complex character, seeming almost to be different people depending on the situation: she can be forceful, even cutting, but also switch gears to become indirect, evasive, or surprise you with her choices. Having a multi-form, multi-function weapon that doubles as a mobility aide encapsulates that perfectly. And Yang... well, do I even need to go into what having the ability to literally punch people with shotgun/micro-missile blasts says? I think we all get that one.
I suppose what I'm saying, in simplest possible terms, is that motivation matters a lot, and needs to be reflected as a continuous thread in what a character chooses and how they express themselves: food, clothes, weaponry, the works.