Cetus doesn't like that Deepcolor, initially, sees nothing wrong with assimilation and brainwashing to suit her own purposes. Of course, Deep doesn't really understand the issues with infringing on the free will of others. She's a seaborn. They don't really have much of a concept of "free will", at least not in the sense that humans do. When Cetus is upset about the very real possibility that his family, especially his father figure Krakii, will someday become assimilated into seaborn and lose their individuality, Deepcolor can only ask him why assimilating would be such a bad thing. Cetus gets VERY upset with her and basically asks her to leave him alone. Deepcolor is confused what she did wrong but leaves. This is the setup to a lot of events that happen later involving Deepcolor learning about the value of individuality, choice, and free will. So she eventually learns just how insensitive she was being by operating on seaborn logic. Deep perpetuating the harm her kind have done out of ignorance is something Cetus does his best to be patient with, but sometimes even he gets frustrated with her.