Hearing Weiss' explanation, Kuroneko asked in a fearful tone, "Wait, we need to drown there?"
Although Kuroneko wasn't afraid of water, he was afraid of drowning.
Well, most humans were afraid of drowning. After all, if a human drowned, they would die.
Weiss replied, "Not 'we' but 'you'. You will swim in the swimming pool and drown there. After you drown in the swimming pool, you can get the Water Authority."
Realizing the implications in Weiss' words, Kuroneko regretted voicing out his complaints. If he didn't complain, then he wouldn't have been chosen.
Although Kuroneko liked obtaining power, he just hated drowning. When Kuroneko was a kid, he almost died when he drowned in a swimming pool. Fortunately, the lifeguards had saved him in time.
It was already a good outcome that he didn't have any fear or trauma towards water.