Gensou Makyou Kitan

There was a man whose luxury cruise ship sank during his honeymoon, leaving him and his wife stranded on a deserted island. However, his wife fell ill there and passed away shortly after. Unable to bear living in the place where his wife died, he rowed out to sea, and while on the verge of death with no food or water, he was rescued by a passing ship. That ship was en route to an uncharted region on a top-secret mission to search for mermaids.