Oyako Kingyo is a set of two boxes that are shaped like stylized goldfish, one big (mom or dad) and one small (the baby). The boxes can be stacked and carried together, held together by the included red elastic bento belt. You could also use them one at a time - the baby goldfish box makes a great sidebox for other bento boxes, and the parent goldfish box on its own is perfect for smaller appetites. The baby box can be put inside the big box for compact storage. 

The boxes are covered with the red, yellow and black goldfish design on the outside, and are black on the inside. The baby goldfish box has a removable inner container. 

(Incidentally, oyako means "parent and child", and kingyo means "goldfish" in Japanese.) 

These boxes are so striking, that they have already been featured in two French bento books!