DO NOT LISTEN TO 1-STAR REVIEWS
Guys, real co-op just wouldn't work for this game. Oatchi doesn't have all the abilities like a captain would at the start, and you have to ride Oatchi constantly, which would be very annoying for the second player. Basically controlling Oatchi wouldn't be very fun for the second player especially at the start when Oatchi can't do much.
Besides, I don't think the Pebble Pitcher is that bad. You can't get in anyone's way and it makes it accessible to younger players who can't ruin the 1st players experience by wasting time or something.
I'm sure if Nintendo wanted to add real co-op, they would. Clearly the game wasn't made with co-op in mind, and I don't think that instantly makes it 1-star. People only like to review a game if they think it's bad, which explains all the 1-star reviews.
Please play the game. It's a masterpiece.