Cetus is usually very calm and rational during arguments. If he isn't taking it seriously, he might be deliberately facetious or sarcastic, or say something just to get a rise out of the other party. But if Cetus is actually arguing, it's probably because he's spent time already thinking about every way this conversation could go and is constantly thinking about his goals here. He'll approach it in a variety of ways, usually changing his style to suit the person he's arguing against. For example, if he was to argue with Deepcolor, he would try to be very calm and rational. She doesn't respond well to emotional appeals or outbursts because of her seaborn nature, so he needs to think more like her and convince with rationalization. But if he were to argue with someone who deeply values others like Skadi, he would appeal much more to their emotions. Cetus shifts his style to one he believes would have the most success with whoever the other party is, usually after careful analysis of their character.

Gladiia is kind of like the final boss for all of his argument skills but even then he struggles to budge her. In the end she has to make the decision on her own, but during his argument with her is one of the rare times that Cetus slips and shows true desperation, simply letting his feelings take over rather than making a calculated play. Gladiia has the power to bring that out of him with her stubbornness, LOL

but yeah basically Cetus is the master of the persuasive essay he can pick an approach and then attempt to appeal to pathos ethos and logos