Under appreciated little visual novel.
It won't blow you away in design or story but it is a satisfying experience if you can overcome the surface level writing style and use of tired tropes from the male protagonist.
Ion and Petako are the two resident mermaids, each have their quirks and charms. Rin is a split personality priestess wanna-be, she attacks the main character constantly and perhaps the weakest element in this title.
With multiple bad endings and a good and true ending.