These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Executive Meddling: Hekikai was originally thought of before Karin. Kagesaki-sensei planned it while she was in middle school but had to change her original idea of Hekikai because the executive didn't like it.
Hollywood Pudgy: Nagisa apparently consideres herself fat and she has taken summer diets that ultimately fail, but she isn't more fat than the rest of the cast.
Ho Yay: Tsukasa was meant to be gay for Tatsuya or at least was pointed to be, as seen in this volume 2's omake. Though, now he's a wholesome fraternal figure to him, some can't stop see the Ho Yay between them. Even Minagi point it once!
Moe: Sheila. Woobie? Check. Cute Mute? Check. A little bit of lost and you can't avoid want to protect her? Damn check.
They Wasted a Perfectly Good Plot: The whole Shizuki's "fishing something more big than mermaids" talking about Demiurge, her identity as the goddess Pistis Sophia and the past of the twins; not to mention maybe a more epic battle between Seine and all the mermaids; and also the thing about if the death of Tatsuya's parents was really an accident or a murder. It's possible Kagesaki-sensei had more history in mind but Hekikai was victim again of Executive Meddling.