Joe is Katsuya Jonouchi's Digital Pet, in the Toei Yu-Gi-Oh! anime. He is based on Jonouchi's Digital Pet from the Yu-Gi-Oh! manga
Eager to win a trip to Australia in an upcoming tournament, Jonouchi trained Joe hard. He continued to train him during school hours, rather than turn the Digital Pet off.
Jonouchi connected Joe with Yugi Mutou's pet U2 for a data exchange. As Digital Pets commonly took after their owners, Joe began to bully U2, like how Jonouchi used to bully Yugi. The two pets became friends afterwards, similar to Jonouchi and Yugi.
After Kujirada got his pet, Devil Master, to eat Anzu Mazaki's pet, Sumomo-chan, Jonouchi connected Joe to Devil Master to battle. Joe initially caught Devil Master with a sneak attack, but was ultimately eaten too. Hiroto Honda avenged the two of them by having Super Strawberry beat Devil Master.
U2 was able to beat Haiyama's pet, after powering-up due to its data exchange with Joe.