Cecilia Reyes has plenty to say. I mean that both figuratively and literally. Reyes is not a woman to keep quiet and do what she's told. She has opinions, and an almost pathological need to share them. She does it to assert dominance, she does it to hide nervousness, she does it to flirt and argue and annoy. She does it both when it's the best possible course of action, and when it's the worst (were it not for her mutant force-field, she wouldn't have lasted five minutes in some of the situations she finds herself). And every single time, even when what she's saying is totally ridiculous - her attack on Iceman whilst he's trying to save her, or lecturing the damn-near-immortal Wolverine over his refusal to wear a crash helmet - it always makes perfect sense that she's saying it.
Obviously, over the entire course of history, our erstwhile "funny books" have considered a tremendous range of topics and ideas. The specific concerns of the mutant line have been well-discussed here, but you can easily find more examples: Spiderman's exploration of the burdens of responsibility and the difficulties of growing up, for example (hence the very-much-not fan-favourite Brand New Day story throwing Peter Parker back into his past rather than risk attempting to find a new metaphor to play with), V For Vendetta's exploration of humanity's desperate need for order, or Midnight Nation's ruminations on the nature of the soul and our place within the world.
Note that there are two strands tangled up in the above formulation. When we say "what does it mean to be a superhero?", perhaps we should say instead "What does it mean to be a hero?" and "What does it mean to have super powers?"
Reyes, it turns out, gives us something to talk about in both cases. We'll start off with the "super" aspect, and move on to "heroes" later on.
Read enough superhero comics in general, and the X-Books in particular, and sooner or later you realise that, broadly speaking, almost every character with superhuman abilities can be divided into one of two groups: those who consider their powers a gift, and those that think of them as a curse. There is some overlap between the two camps, yes, but no-one with any experience in comics should have any trouble naming a half-dozen characters from each category.
There are, of course, characters for whom their super/mutant powers are not necessarily all that aid them in fighting the good fight. Cyclop's leadership skills and tactical acumen are both arguably worth more than his concussive eye blasts to explore and utilise their mutant gifts. Their secondary talents became obvious later. Strange became the Sorcerer Supreme only after he lost his ability to be a surgeon.
Cecilia is different. Cecilia is the answer to the question you'd never thought of. What if preternatural powers weren't a gift, or a curse, but a supreme irrelevance?
This allows Reyes to be a mutant second, and something else first; in this case, a doctor. Hardly the easiest thing in the world to become for a Bronx-raised Puerto Rican whose father died in a fire-fight, but nevertheless she perseveres. Whilst Xavier and his coterie were fighting Sentinels and Factor Three, Cecilia was fighting to become a doctor, and at every point along the way, with every agonising step forward, she was doing it without her powers. Not because they made it harder to reach her goal, but because they made no difference whatsoever. To make use of an analogy, Nightcrawler, Beast and their fellows are trying to figure out what to do now they've been outed. Cecilia is figuring that no-one need ever know.
That's an interesting take on the mutant issue in any case, but it's particularly fascinating with regard to Cecilia because she strives to be what in the real world we would have no hesitation in labelling a hero; one who saves lives with no regard to themselves. The fact that her ability to generate force-fields reflects her constant need to throw up shields against everyone she meets is another nice example of a power reflecting a personality rather than being entirely separate from it, but it's not the point. The point is that the shield protects her but doesn't save her from pain. When she's shot, she still feels like she's been shot. Using her power, each and every time, is a sacrifice. But the very moment she can interpose herself between someone else and harm, she does it without a second thought. She acts as a shield for those she barely knows. She exchanges their wounds for her pain. Because she's a doctor, and that is what they do.
In other words, the only time she makes use of her powers, it's to augment her role as a healer. The one time it isn't, the one time she kills a man to save another's life, she starts to hyperventilate, before starting down a hideously destructive path that is equal parts redemption and repression. Perhaps some superheroes might exchange a villain's life for a comrade's, might recognise that the world needs one more Nightcrawler far more than it needs one more Jaeger, but a doctor cannot make that call (q.v. Voyager's best episode). Rather than being defined by her powers, she tries always to have her powers operate within the definition she gives herself.
Ultimately, though, what in that differentiates herself from a hero anyway? Certainly not a fundamental aversion to killing. In truth, there are a lot of different ways you can explore the meaning of heroism in superhero comics. Stripping the protagonists of their powers is a common one (it's happened in to the X-Men alone more times than can be easily counted), so as to demonstrate that the good guys won't give up fighting for what they believe in just because they've suddenly become like everyone else. Introducing supervillains with equivalent powers, histories or genealogies can be effective too; allowing writers to explore the choices and events that led to a particular character choosing to fight on the side of the angels (this can also work by introducing "bizarro" characters from other dimensions who took the opposite path despite ostensibly being the exact doubles of our heroes).
Once again, Cecilia offers something new (and not simply because she refuses to take a code-name; remaining Doctor Reyes from her first day on the team until her last, which comes far too soon). Cecilia's conflict is born from the fact that she's already a hero, whether she acknowledges it or not, but the scions of Xavier are pushing her towards becoming a hero of a different stripe; a stripe which holds no interest for her whatsoever. The X-Men try to prove to her that there is no shame in being a mutant, but what they need to be doing is demonstrate to her that being an X-Man is of greater worth than being a doctor in a New York hospital. Which it might well be, given how often they've saved the world. But it's not something you can just state and hope will be believed.
Next month, we're back to mass-murderers, and an attempt to puzzle out why anyone thought a serial killer could join the team without actually bothering with anything so awkward as atonement or apology.