Zexion is an interesting case of sass because the reason he comes off sassy is that he says rude things but he says them in an ostensibly polite way. He never insults anyone straight out.
Some examples (note: some of these are from the original CoM which has a slightly different script but the changes are small)
What he says: I think eavesdropping is intrusive. Why are you even here? You and Xaldin were tasked to recruit new members. Have you forgotten or were you procrastinating?“
What he actually means: Xigbar you lazy, nosy shit get back to work
What he says: 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
What he actually means: Don’t be a lazy ass Roxas
What he says: "Don’t I even warrant a hello, Lexaeus?”
What he actually means: Rude much Lexaeus?
What he says: 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.
What he actually means: You’re an ass
What he says:
Zexion: Roxas, you and I and all the Organization’s members are what we call
Nobodies.
Roxas: Well, that’s not very nice.
Zexion: With a capital N.
What he actually means: Give me strength to deal with this fantastical moron
What he says: Nice to see you too, Vexen. It’s such a shame. The Organization used to be the rope that bound us together./Nice to see you too, Vexen. You know, it’s deplorable… The Organization used to be the rope that binds us. And now it’s full of kinks.
What he actually means: Y’all rude
Now granted not all of these are sassy but it does play into the idea that Zexion is not a frank speaker.
And on top of this in Japanese Zexion always speaks in polite form even when social convention says he doesn’t need to (like when he’s talking to Roxas who is both younger than him and his subordinate and also to people he’s obviously known for a really long time and is likely super familiar with).
Like if you watch the Japanese cutscenes you’ll see a lot of ます at the end of his sentences which is used in polite verb conjugation
A conjugation chart with sample stem 「遊び」ます conjugationsStem+ます
Plainます遊びます
Negativeません遊びません
Pastました遊びました
Past-Negませんでした遊びませんでした
He also doesn’t drop the です at the end of sentences. です means to be and often times it can be dropped or replaced in a sentence when you’re not being formal.
http://www.guidetojapanese.org/learn/grammar/polite
btw that last can literally translates as “Is there a message of greeting? Lexaeus.” Which means “aren’t you going to greet me Lexaeus?” And it has です and か at the end of it so it’s said politely.
か is the question particle that you add at the end of a sentence to make it a question. It can be dropped in informal speech…you can drop a lot of things from a sentence is Japanese. Like hell if it’s obvious what you’re talking about you can drop the subject/topic from a sentence. It’d be like me in English going “My cat is black. is fat” instead of “My cat is black. He is also fat”. (not the best example but you get the idea)
And finally someone who went to Japan told me that “The more you say in Japanese the politer you’re being” meaning that the more words/sounds it takes for you to say something the more polite it probably sounds. Which given informal forms are usually shorter than formal forms make sense. And we all know how much Zexion talks.
So case in point, despite saying impolite things, Zexion sounds polite/formal.
It makes for interesting sass as most sassy people are much more direct about their sass. It also makes for more clever sass as “hey I’m not sassing you because it sounds polite”.
It also plays into Zexion’s personality of working from behind the scenes. He never insults someone directly, he does it backhandedly. He’s kind of rude and yet he hides it behind politeness.