Despite having no familiarity with Gaelic mythology, there is something incredibly nostalgic about this game. The soundtrack, the choice of colors, and the traditional artwork / sprites all lend to this sort of dreamlike, surreal atmosphere... which puts us directly in the shoes of Amelia, who probably spends the whole duration of the game not quite believing in this reality yet allows herself to be swept along the wave. The way that the narrative jumps around the chronological timeline also adds to this effect, yet the storyline manages to remain coherent.
I think you really nailed the fundamental appeal of mermaid fairytales: the thought that there exists a world out there far removed from our mundane world of paperwork, corporate, and people; and that maybe - just maybe - it's within reach, as easily as stepping into the water. And I love that this escapist fantasy applies not only to Amelia (whom you would expect from the premise of the game alone), but also to Mairi (once you learn her backstory).
Mairi is such a captivating character: refined, untouchable, cute, vulnerable, predatory, manipulative, and tragic all at the same time. I like the parallels between her and Amelia, and the way they connect over their feelings of... being a "fish out of the water" (sorry).
Lovely work!
P.S. Chibi Mairi is adorable