For reference, should it be needed. I tried to keep it short, but it got longer than I meant to. I'm bad at keeping this short, sorry. I just can't shut my goddamned mouth when I talk about this series.
Axl is from the Megaman X series, which is about a bunch of superadvanced robots beating the shit out of each other, supposedly over the lives of the human race but oddly enough there is only one human character and he hasn't shown up since a brief mention in the instruction manual four games ago. Whatever.
Basically, humans built a race of so-called "reploids," robots with free will, emotion, and the ability to make their own decisions. Some of the reploids decided killing humans was a swell idea. These are "Mavericks," and the organization that sprung up to fight them are the "Maverick Hunters." The leader of the Mavericks is a former Hunter named Sigma, who is something like a robotic Rasputin in that he's fucking insane and will not stay dead. The main character of the series is X, the Hunter who pwns Sigma's ass repeatedly and with style. His best friend, another Hunter named Zero, butts in and steals a lot of spotlight halfway in.
Axl doesn't show up until the seventh game in the series, so for the purposes of knowing what his deal is, the first six games aren't that important. Just know that X spent a lot of time angsting, and Zero spent a lot of time getting killed and resurrected. Also, there's a virus running loose in the world, known variously as the Maverick/Sigma/Zero Virus, depending on the strain. It makes reploids go Maverick. (The series also forgot somewhere along the line that logically any reploid can decide to kill people and become a Maverick, virus or no--more on that later. Continuity is not a strong point for this series, what can I say?)
So, lots of fighting, lots of killing, Zero dies twice, Vile dies twice, Sigma dies like six times, blah blah blah yada yada yada. Flash forward to Megaman X7.
X, in a fit of extreme emo, quits his job to try and work for peaceful solutions. Since X was apparently doing like sixty percent of the work for the Hunters, crime goes up, and bounty hunters start filling in the gap. Foremost among the bounty hunters is the Red Alert Syndicate, who used to be pretty decent, as bounty hunters go. But THINGS ARE CHANGING, which leads Axl (who is a member) to decide that fuck this shit, he's goin' to Disneyland. Or to become a Maverick Hunter. Whatever.
Axl runs off, they send people after him, he runs into Zero, who hauls him into Hunter HQ so X can bitch him out. While X is being an ass and Axl is busy fanboying X and Zero, they get a call from Red, the oh-so-creatively-named leader of Red Alert, saying that they want Axl back and there will be Big Trouble if they don't get him. Axl and Zero go out to fight the Red Alert higher-ups, while X sticks around the base and listens to Linkin Park and cuts himself or something. (Can you tell that I think they made X way too whiny in X7?)
In between slaughtering all of Axl's old buddies, there are a bunch of little scenes in which we find out what the hell is really going on. Axl has this nifty and unique ability to copy other reploids and take on their forms and abilities, which he used to use IN THE SERVICE OF JUSTICE but then A MYSTERIOUS INDIVIDUAL began to gain influence over the syndicate, abusing Axl's powers for ill. Axl has no memory of his past before Red Alert, because MYSTERIOUS ORIGINS make him COOL or because Capcom was too lazy to write the rest of his backstory.
Somewhere in here X decides to quit being a pansy and join the fight.
The trio finishes killing off most of the members of Red Alert, and heads for Red Alert's base to fight Red. They kick his ass, Red and Axl have a Touching Moment of Bonding, because Red is not evil, but was being blackmailed, as the MYSTERIOUS INDIVIDUAL infected all of the other members with the virus as leverage against him. Red dies, the boys move on, and as anyone with half a functioning brain cell has guessed long ago, the MYSTERIOUS INDIVIDUAL is Sigma in disguise.
They kill Sigma, but in the ending movie, Sigma pops back up, sprouts tentacles, and gropes Axl. Axl then shoots Sigma in the face, and he goes flying out a window, dying. Again. Supposedly.
Axl becomes a Hunter, and somewhere along the line X and Zero stop being total dicks, and the three become Bestest Buddies. The government also start mass-producing "new generation reploids," for which Axl is the prototype. They all have copy chips, and are incidentally immune to the virus. And all of the new gens built after Axl have the data of many dead reploids from the past preloaded into their copy chips (if Axl needs data to change into something, he has to go out and get it himself before he can use it). Even Sigma's data is in there, but since they're immune to the virus, nothing can go wrong, right?
Right?
Vile (old enemy who died five games ago) pops up with absolutely no explanation whatsoever and kidnaps Lumine, a new gen who is in charge of the space program. A bunch of new gens go Maverick, and the good guys freak out and wonder HOW THIS CAN BE when the new gens are immune to the virus, thus forgetting the whole FREE WILL thing provides an OBVIOUS EXPLANATION but let's not worry about the DETAILS. So they go out and kick a lot of ass, and in the scenes in between there's a bit of OH NOEZ AXL IS A NEW GEN WHAT IF HE GOES CRAZY TOO.
The new gens are apparently being led by Sigma. As if we expected anything else. Yawn. So the guys go to the moon to fight Sigma, and kick his ass, and the plot strongly hints that this might actually be the LAST TIME, and he may really be DEAD FOR GOOD. And then something really amazing happens.
Sigma is, for once, not the final boss. The plot suddenly remembers that Lumine exists, and he pops up and attacks the Hunters, then gives a speech about how he's going to wipe out everything but the new gens, because evolution is the shiznit and humans suck and just get in the way anyway. (Axl also does something unprecedented; he shoots Lumine in the middle of the Traditional Villain's Monologue. There's a reason I love this kid so much.)
Our heroes respond by beating the shit out of Lumine. ALL LOOKS WELL, but then Axl has a STUPID IDEA and goes to poke the body and be sure he's really dead, at which point a GIANT TENTACLE pops out of Lumine's chest and BITCHSLAPS HIM IN THE FACE. X and Zero finish off Lumine, and X carries the now unconscious Axl as they head back to base and it DOES NOT LOOK SLASHY AT ALL, REALLY IT DOESN'T.
And then there's this ominous little bit at the end in which there's something glowing in Axl's head where the tentacle hit him, which most of fandom interprets as a sign that Axl has Lumine's data running loose in his systems now and is thus going to go insane and/or Maverick in the inevitable sequel.
Other relevant details: Axl, if anyone hasn't noticed, is a total gun nut. Also, his Japanese voice (provided by Takayama Minami) is the fucking cutest thing ever.