I see your point.A nice update, but the interaction with the mermaids was kinda annoying. Not the threesome part, but the talk about finding a way to get them to the school in case they need to give a warning. I would have liked it restated that we want to introduce the mermaids to the rest of the girls. Felt kinda like reducing the two girls to simply being guards. And it's not fair on them to be separated from the rest of the harem more than is necessary
But this is an issue that MC can't fix. At least he doesn't know how yet. Nor do they know a way. Being limited to only a few minutes out of water makes things difficult for them. But it is something we will eventually solve.