Author's Note: The whole "Riku Replica/Axel/Zexion" scene in Chain of Memories never did make any sense.
So here's a somewhat-silly retelling of it that attempts to make some sense out of it without making Axel look like a complete bastard who randomly changes personalities at a moment's notice (seriously, look at Regular CoM Axel vs. Zexion's-Death-Scene Axel vs. KH2 Axel. If they didn't look identical, you wouldn't even be able to tell they were the same person.)
There's also a slight effort to make the Riku Replica look like less of a moron, but that's a bit harder than making Axel look sane, so... yeah...
That One Time, When Axel Got Drunk
Axel stumbled into an empty meeting room, still carrying a large bottle of something alcoholic in one hand. The Riku Replica, who had no idea what was going on, was following a few feet behind him, occasionally trying to peek at the label of the bottle to see what it was.
"Hey, Axel," he said, "Can I have some of your drink?"
"No," Axel said, waving the bottle around in the air and looking like an absolute drunken fool, "Thish shtuff, ish... not for kids, yo... ish too shtrong for teh kids..."
The Riku Replica gave him a funny look as he swung the bottle around for a few seconds more, then finally turned back around and continued walking--or maybe "staggering" was the better word--into the meeting room. Why was Axel acting so weird? Was it something he ate? Or was there something wrong with the stuff he was drinking?
Maybe he accidently got some of Vexen's chemicals in that bottle, the clone thought, That'd make him sick for sure...
But the spiky-haired man didn't really seem sick--at least not yet. He just seemed like he was having trouble walking, and pronouncing words correctly, and... well, everything else. He also didn't seem to be aware of how silly he looked, staggering around and occasionally waving his bottle in the air in between taking drinks from it.
"What's in the bottle, anyway?"
"Ehh... ish nothin' little kids need ta know about," Axel slurred, "Nothin'... nothin' important at all, jusht teh... whoopsh, almosht told ya..."
And then, suddenly, a dark portal appeared on the other side of the room, and a short, blue-haired man came flying out of it, catching himself with a hand and a knee just in time to avoid falling flat on his face.
Zexion slowly stood up and brushed himself off, seeming shocked about something. Axel didn't notice thanks to his intoxication, but the Riku Replica spotted a large cut in the chest area of his cloak, revealing a small part of the clothes he was wearing underneath (which just happened to be a Weird Al Yankovic t-shirt, which Zexion was often seen wearing when not in uniform.)
The Riku Replica just watched and attempted to listen as Zexion muttered several things to himself, clutching his chest in pain. He said something about Darkness, and then suddenly his voice became a bit louder and he yelled out that something was, in his own words, "NOT POSSIBLE!"
And then, Zexion finally noticed that he wasn't alone in the room. His eyes (or, more accurately, his eye, as only one was really able to see very well thanks to his odd haircut) wandered across the room, first spotting a familiar sight--Axel, swaying slightly as he stood on the other side of the room, holding a 40-ounce bottle of something alcoholic with one hand while the other hung limply at his side. And then, he turned a little to the right, and...
"Waaaah! Riku?!", he squeaked, backing away slightly and nearly falling over. He then remembered that he had just escaped from the real Riku, and that there was no way he could have caught up with him already--so it must be that clone that Vexen made instead.
"Oh... oh yes, of course!", he said, realizing that he had nothing to fear from the "fake" Riku, "Vexen's replica. Good thinking--we can use this Riku to defeat the real one."
He noticed the Riku Replica glaring at him for a second, and realized that he probably should have phrased what he said a little bit better--the Replica never did like being referred to as a "fake," regardless of the fact that he essentially was--even more now than before, thanks to Naminé modifying his memories to resemble those of the original Riku more closely.
"Axel?", Zexion asked, turning toward the spiky-haired man and wondering what was going on. "Are you drunk?"
Axel confirmed Zexion's suspicions by taking a massive gulp from his bottle of alcohol, then turning toward the Riku Replica and speaking with a heavily-slurred voice.
"'Ey, Riku," he said, "Musht be... kinda hard knowin' you're not teh real Riku... y'know?"
The Riku Replica gave him a funny look, then glared at him a little as well. He was about to say something else when Axel leaned closer to him and acted as if he were whispering, even though he was talking just as loudly as before.
"I bet you'd like ta be real," Axel said, following it up with a loud belch that sent a noxious blast of beer-breath into the clone's face. The Riku Replica staggered back a little, holding his nose, and thankfully Axel pulled back away from him a little and turned back toward Zexion.
"Um... yeah," the Riku Replica said, deciding to play along with whatever Axel was doing. After all, some people get angry when they're drunk--he didn't want to accidently piss Axel off.
Axel wobbled a little, then turned back to the little silver-haired boy once again. The Replica braced himself for another belch, but it never came. Instead, Axel started talking.
"Well, you can... all ya need ish... er," Axel said, hiccuping several times in the middle of his sentence, "All ya need ish shtrength... that teh real Riku don't have, y'know? So you can be... a new pershon, not jusht anotha Riku... or somethin' like that..."
Zexion looked at Axel like he was insane, brushing his emo-looking hair out of his face so he could give him the "you're-friggin'-crazy!" look with both eyes rather than just one. Axel didn't seem to notice, however, and just kept wobbling around in the place where he was standing.
"Axel!", Zexion said, pointing to the drunken porcupine-head, "What are you telling him?! That doesn't make any sense!"
Axel staggered closer to Zexion, patting him on the shoulder, and then backing up a little and pointing toward the shorter man.
"Y'know," he said, turning to the Riku Replica while continuing to point at Zexion, "I bet he's as good a plashe ta shtart as any."
The Riku Replica looked at Axel, looking very confused. What in the world did he mean by that? Everything else was at least understandable, though slurred and often interrupted by hiccups, but this was just ridiculous. How could Zexion help him get stronger? Everyone knew Zexion was the wimp of the Organization.
"Have you lost your mind?!", Zexion yelled. The fake Riku was thinking essentially the same thing, though he said nothing. And then, Axel finally offered his bottle to the little boy, despite his previous warnings of the bottle's contents being "too shtrong for kids."
The Riku Replica took a big gulp, and suddenly everything made sense, though the room looked a little more wobbly than it had before and it was becoming harder to focus on anything... and Zexion now looked kinda like a girl. "Of course!", he thought, "Axel's saying that all I need to do is stab Zexion with my sword and try to absorb his power!"
"Shorry, Zexy," Axel said, patting Zexion on the back after taking his drink back from the kid, "Shaving--er, I mean shaving... no wait, SHAVING you doesn't sheem half as... half as en... ter... tain... ing..."
Axel seemed to have great difficulty pronouncing "big words" now that his blood alcohol content was at a point that would cause the average human's liver to fail just from the thought of it.
"As... er, where was I?", he continued, forgetting what he was going to say for a second before catching himself, "Oh yeah, as obsherving Sore and Reek--er, I mean, obsherving Sora and Rikku... er... wait a second here..."
Zexion wasn't sure whether to groan or continued panicking, and the Riku Replica began tapping his foot on the floor in between wobbles. Thanks to the beer goggles he was now wearing, Zexion looked like a somewhat attractive girl, so he was staring at the blue-haired man's chest to pass the time while waiting for Axel to remember what he was trying to say.
"Oh yeah, I gots it now," Axel said, standing up and crossing his arms (though still wobbling occasionally), "Shaving you doesn't sheem half as en... ter... tain... ing as obsherving Sora and Riku!"
The Riku Replica grabbed Axel's bottle once again, emptying the last of it with a massive gulp, and then drunkenly charged forward with his Soul Eater held out.
"No... STOP!!!", Zexion yelled, but before he could "STOP!!!" the little clone boy, the Soul Eater jabbed into him and his body began to glow in a very weird way that was entirely not normal for a Nobody's death. A few seconds passed and Zexion suddenly disappeared--without dissolving into black stuff like other Nobodies, oddly enough--leaving Axel and the clone alone in the unused meeting room. And the Riku Replica lifted his sword up, balanced it on his shoulder, and began to walk out.
"That's funny," he said to himself, "I don't feel any stronger now... oh well, time to go kill the real Riku so I can stop being fake... or somethin' like that..."
And as he left the room, Axel finally became too drunk to stand, collapsing onto the floor and lying there, unconscious and drooling all over.