Through extensive research and studying of the Re:Chain of Memories, Kingdom Hearts II Final Mix, and 358/2 Days cutscenes, along with his appearances in the Kingdom Hearts mangas, I have compiled together every line that Zexion has ever said.
Kingdom Hearts Chain of Memories
"Don't I even warrant a hello, Lexaeus?"
"Nice to see you, too, Vexen. It's such a shame. The Organization used to be the rope that bound us together."
"Visitors. I picked up two scents in the castle's lowest basement. One of them was Maleficent."
"If you would let me finish...The scent belonged not to the real Maleficent, but to a very convincing double. But I truly cannot say much beyond that since the double is no more. Our other visitor saw to that."
"I do not know for sure...But the scent was very similar to that of the Superior."
"Now, what to do?"
"I have identified the scent. It is...Riku."
"His existence—it was once doubled in darkness..."
"What I want to know is why he appeared in Castle Oblivion..."
"Sora is in the castle?"
"Without even bothering to consult us."
"Naminé’s powers are being used to shuffle his memories as we speak. Marluxia may well succeed in getting his puppet. Sora would be a valuable asset to the Organization."
"But Marluxia and Larxene’s actions, they...Leave me uneasy..."
"Vexen should take care of this. His replica is soon to be completed."
"So we must tell him. Isn’t it better that Vexen clean up the mess than leave it to us?"
"Yes, his scent is gone. Axel struck him down...Something I find deplorable. Agents of the Organization striking each other down."
"But we can not eliminate Sora, can we?"
"Riku...Of course."
"Lexaeus is gone as well..."
"I thought perhaps it might be you."
"Yes, we were going to set him off against the traitors...But with Marluxia gone, there is no more need. He is nothing, but a nuisance, now."
"You know that is not how I do things. Tell me, did you obtain the data on Riku's home?"
"The keeper of this castle, Marluxia, has just been felled by the Keyblade Master."
"Yes. Want to see him? But...Can you face him?"
"The world of darkness and Ansem's shadow still nest within your heart. Do you plan to face Sora like that? Even after what you did to him? Are you not ashamed? "
"Sora's fate is to battle the darkness. He must oppose anyone who hosts the dark. In other words, it’s you. If you don’t believe the words I say...Best see the truth with your own eyes."
"Yes, it is your home."
"Surely you must've known this was going to happen. And in those worlds, you met only dark beings. That’s all that’s left in your heart: dark memories. Your memories of home are gone—each and everyone."
"And who threw away those friends? Maybe it’s your own actions that you’ve forgotten. You destroyed your home!"
"All of the islands you grew up on were sundered, scattered! Many hearts were forever lost to the darkness! Because of what YOU did! You hated being an islander, so you opened the door to darkness and destroyed the islands! It was YOU! You were pulled into the darkness then, and now you belong to the darkness! You should look—look at what you truly are!"
"Impossible! How is it that you found me when you were there in the light?!"
"This is absurd...! Then I shall make you see...That your hopes are nothing! Nothing, but a mere illusion!"
"After all your protests, you’re still like us, on the side of darkness!"
"When did that happen? You were always terrified of the dark before-"
"What IS he!?! No one’s EVER worn the darkness the way that he does! It’s impossible!"
"Oh, yes. The replica, of course. We can use this Riku to defeat the real one. Axel?"
"Axel! What are you saying to him?!"
"You can't do this!"
Kingdom Hearts II Final Mix
"What's all the fuss about?"
"At the usual place."
"If it's urgent, why don't you go and see?"
"What are you doing, eavesdropping like this?"
"The mission assigned to you and Xaldin was to look for new members.
"You shouldn't be able to afford wasting time around here."
"Then please rest fully. I have work to do for today so I'll be going..."
"What of it?"
"It seems you really enjoy eavesdropping."
"I simply want to concentrate on my assignment. You too should concentrate on your real mission and collect more members."
"We must hurry with the preparations for our new quarters... 11 Organization members is not enough."
"We've been told that-"
Kingdom Hearts 358/2 Days
"Your mission today is to eliminate a set quantity of Heartless."
"The Organization may call upon you to meet other objectives--perform recon, for example."
"But regardless of the task you have been given, your primary orders still hold."
"You and that Keyblade of yours serve us best by collecting hearts."
"Correct. Today, however, the two happily coincide."
"Leave, already? I, for one, would apply myself a bit more."
"Yes, yes, you did as you were asked. Mission accomplished... but..."
"As you can plainly see, there are still Heartless wandering about."
"You don't have to eliminate them all. It's your choice."
"Just like I don't have to respect you for slinking back to the castle while there's still work to be done."
"And if that doesn't matter to you, just remember the Organization rewards those who make the extra effort."
"Much Better. I trust you'll exhibit equal diligence in your missions going forward."
"All right, now that the mission is over, do you have any questions?"
"Yes...? Kingdom Hearts will complete us. That's the Organization's goal."
"Roxas, you and I and all the Organization's members are what we call Nobodies."
"With a capital N. It's a name, for those of us who are missing a vital piece of who we are: our hearts."
"Correct. Like all of us, you entered the world without one. But you can help us get them."
"Kingdom Hearts is made of the very things we lack--a multitude of hearts. It has the power to complete us."
"Are you starting to see why you're so important?"
"Each of us has a vital role in the Organization. Yours is collecting hearts."
"Well, I just hope we can count on you to "get it" done."
"Any more questions? Then we should be getting back. Come on."
"Surely... you must have know that this was going to happen"
"Because, in your memory, you've been to a number of worlds before you came to this one."
"And of course, in those worlds the only beings you met were the dark kind."
"That's all that's left in your heart: the darkest memories."
"Your memories of home are gone--every one."
"And who threw away those friends? Maybe it's your own actions you've forgotten."
"It was you who destroyed your home!"
Kingdom Hearts Chain of Memories Manga
"I made these pickled vegetables"
"One is Maleficent... And the other smell is..."
"Um... can I continue?"
"...The other smell is... Riku!"
"I'll look into it. But... The scent is very similar to the superior's. Exactly the same. If I may say."
"Riku once shouldered the darkness. Perhaps that made him half-dark"
"That is why he smells like the superior. Not because of perfume"
"He's persistent when he gets excited."
"But I wonder why he showed up in Castle Oblivion? Nobody led him here..."
"It seems like Vexen has disappeared..."
"People with the same existence are supposed to work together... what a wretched thing."
"The burden of chores will increase"
"It's becoming quite clear that Marluxia is planning to take over the Organization"
"If we don't get serious... we'll disappear at this rate."
"Lexaeus. Capture Riku."
"...Lexaeus... You being taken, as well.........served no purpose."
"If Marluxia gets Sora, then I will surely be erased, as well."
"If I can't get Riku to come to our side somehow... just what will become of the Organization's future?"
"You know, as you are now, you are unable to meet anyone."
"No, it would probably be more appropriate to say that you don't have the qualification to meet."
"Look, your true form."
"That's right, that's the old you."
"Only yearning for other worlds, you rashly opened the door of darkness."
"It's your fault our island disappeared!"
"You lowly being of the darkness!"
"I'll erase you with the power of light!"
"That's right, Riku. Recognize where you stand. Because preparations for your reception are done!"
"That's right. You are from this side."
"My name is Zexion"
"Don't you see? That power will be helpful to the Organization."
"Cut off! Literally..."
Kingdom Hearts 358/2 Days Manga
"When I was born into this world, I was lacking a heart... or so they say."
"It's not impossible."
"He's not like us... because he doesn't have any memories of before he was born."
"Without a "heart" or "memories" it'll be awhile before he shows real reactions to anything."
"Beautiful, isn't it?"
"The "Hearts" you release with your keyblade are gathering up there in "Kingdom Hearts""
"To complete it and unite with it is the goal of our Organization."
"It's the way for we who lack "Hearts" to become complete beings."
"In any case, I'm number 6, Zexion."
"I made some fish, please take it in place of a business card."
"That Demyx has gone off somewhere again...It'll be his neck."
In Battle
"Go!"
"There!"
"Thank you."
"Your memories shall be mine!"
"You should share your power."
"Looks like I have enough."
"See my illusion!"
"Your end is near!"
"You think you can be forgiven?!"
"You brought it upon yourself!"
"What is this?"
"I feel so bad..."
"I may have been careless."
"Have I...been defeated...?"
Impressive, right?