Triton of the Sea Vol 1

From the Digital Manga edition

The ocean holds many tales. Tales of mermaids, of underwater kingdoms, and of fantastical beasts lurking in the deep. Spurred by these tales, Kazuya sets out to find the truth, but what he finds is a baby?! Not just any baby, the baby Kazuya finds is Triton, the last of a once mighty and proud race of people from the sea! Triton seems human, but unusual and terrible events begin to happen with all those around him. Who is Triton, and why does he bring misfortune to everyone around him?

Source: Anime News Network Encyclopedia