Source is a manga called Crimsons
https://myanimelist.net/manga/35047/Crimsons__Akai_Koukaishatachi
The character designs are something else
Maybe some fish isekai?
Well it has japanese katakana in it
Oh slaps forehead Of course It's from a manga! Case closed everybody.
And fish live in the water, so we can narrow it down to a Japanese body of water. I'd wager we're looking at the Pacific Ocean here.