Seriously though!! Like that should have been the first clue that the potion was a failure (｡ŏ_ŏ)
There needs to be no logic ^.^
I think that the potion was still in effect, like it changed his outer appearance but it hadn't yet changed his magic or ability to breath underwater. The potion was a failure anyways so that could always explain it I guess.
porn, you know, don't always have logic ... very often, in fact ╮(￣▽￣)╭
I got a question how the fuck can he breathe in water and he just turned human?! Wouldn't he drown or die? How deep are they in the water? I love this manga but some of it doesn't make any sense.