The organ that belongs in the digestive system is the stomach.

Here's why:

* Digestive System: The digestive system is responsible for breaking down food into nutrients that the body can absorb and use.

* Stomach: The stomach is a muscular organ that mixes food with gastric juices, which contain enzymes and acids that help to break down food.

Let me know if you'd like to know more about the digestive system or other organs!