Fisherboy Gonzui

(from ebookjapan):
This maritime action tale follows the exploits of a black boy named "Gonzui" who washes ashore on a penal colony island after the sinking of a slave ship.

A black boy on a sunken slave ship drifts across the sea in a large barrel and washes ashore on a penal island to which convicted criminals are sent. The black boy, suckled by Azusa, a woman who has lost her baby, and names him Gonzui, is chased by Ryu, who controls the island, and he falls off a cliff with Azusa. ......?