Kai ōi is a Hawaiian term that means "sea eggs." You might also know them as "sea urchins." They are little spiky creatures that live in the ocean and are related to starfish.
Just like people eat chicken eggs, some people in Hawaii like to eat sea eggs! In fact, sea eggs are a traditional food in Hawaii and other parts of the world too.
When people eat sea eggs, they first need to catch them. They do this by diving into the ocean and finding them. Then, they carefully crack open the spiky shell to reveal the edible part inside. This part is called the roe, and it's soft and gooey like jello.
Sea eggs might not look very yummy, but some people think they taste really good. They are sometimes eaten raw, like sushi, or cooked in different ways. Some people put them in soups, stir-fries, or omelets.
So basically, kai ōi are sea urchins that are caught in the ocean and eaten by people in Hawaii and other parts of the world.