Easy. If there was one word Axel would use to describe Xion, it was easy.
It was easy to corner her.
It was easy to get her alone.
It was easy to get her clothes off.
It was easy to make her give her up.
It was easy to make her orgasm.
It was easy to make her keep quiet.
It was easy to do it again and again and again.
Axel didn't know if Xion was naive or truly innocent. Either way, it didn't matter to him-he got what he wanted just as always. Xion was a quiet and shy girl, the opposite of Namine who was merely antisocial. At least Namine had initiative and powerful will. Her sister didn't have a spine to be seen and just let everything happen to her. In his own way, Axel would stand up for her. He'd make sure nobody picked on her or did anything mean to her...but this was only so he could have her to himself. He liked his goods undamaged.
She most often would be found taking photographs of random things around town, so he'd hide in plain sight and wait for her to see him. It never took long for that to happen. Xion would have her back turned and suddenly shiver and turn around looking every which way until she saw him. She would smile sheepishly and walk up to him, submissive and eager to please. And then he would have his way with her.
She doesn't say anything. If she does speak it's usually the "ouch" or "that hurts" in response to his touches. He usually ignores her and keeps going. But even Axel knows he can't get away with abusing her, so he makes sure to treat her well afterwards. He knows the right words to say (when he speaks), and does all the right things in secret.
Xion doesn't know about his exploits with her sisters. Sometimes he's not even sure if she knows her sisters exist. She seems like a doll most of the time, only she can move on her own. She's even more mysterious than Namine, but he almost feels like he can trust her...almost. He still won't tell her anything. Sometimes he gets this feeling that she wants him to tell him something important, but then he ignores everything as usual. Life must go on.
...
Today he notices Xion's eyes. At first it was nothing spectacular about the violet orbs, but then something about them changed. Maybe they didn't change, it was likely they didn't. But he suddenly had this feeling they were watching him. And he was right! Whenever they were together, Xion never stopped watching him. It was subtle, barely the bat of an eyelash; but it was real. She was watching him.
Where Namine saw through him, and Kairi saw past him, Xion was looking right at him. And he didn't like it at all. Was she aware of this? Axel could only guess, but he wasn't going to ask her anything. What in the world was going on? He does her doggy style so he doesn't have to look at her. He even goes farther and blindfolds her. He seriously is starting to hate those eyes.
Her face starts to hold questions, but she won't ask them. Xion won't ask questions. Her expression rarely ever changes save for when they're actually doing it. Then she gets all kinds of happy. She doesn't thank him when they're done, he does the thanking. Axel thinks he'll have to get her something soon, a present perhaps. He thinks that he shouldn't spend so much time with her, even though she says nothing the when stuff happens. He really just wants to get away from her.
Xion senses this and backs off of him. He's already finished up and is getting ready to leave. He doesn't see her for a few days, that's a good sign right? Maybe, maybe not. He doesn't think about it. He avoids all three of them for about a week or so and not necessarily willingly. They had a death in the family. Nobody bothers his phone at all. He is a bit relieved.