Umi Monogatari starts to impress me not only for its visual animation and characters' design, but also because the narrative storytelling focuses on a
slice-of-life approach intertwining fantasy, mahou-shoujo genre.
I'll tell you that both the soundtrack and situations are not typical in contrast to other magic girls like
Sailor Moon or
Pretty Cure, among many others.
For example, most of the music employs soft, jazz melodies to depict the everday instances of Kanon, Marin, and Urin at both the sea and the island.
When Sedna's evil aura or minions manifest around the vicinity, the soundtrack doesn't use music or tunes that feel like the stereotypical evilness song filled of ethereal and haunting motifs.
It is a sort of a soft jazz which narrates that the girls have found themselves into a pinch.