Biography
When Jou first came to the digiworld, he found a Bukamon waiting for him. He freaked out immediately, and Taichi found him running around with Bukamon hugging him or something.
When the digidestined were splitted up from Vile Island, Jou winded up lost with Sora. Apparently, Sora seemed somewhat concerned about Joe's apparent need to always tag behind and started telling him to act more bravely. With a plan from Gomamon and Biyomon, they made him the new leader. Then they were launched at by Bakumon and his "mind over matter" technique worked. With renewed sense of bravery, the two set back to Vile Island to fight Devimon. I guess in a sense, he admires Sora if he wants to stick behinds.
At the beginning of the Etemon Saga, Joe was the second to recieve his crest, the crest of reliability. Though it was strange that he obtained this crest, he nonetheless did it to help Gomamon digivolve to ultimate.
When the digidestineds returned home, they immediately went to their homes. Most of them lived in central Tokyo, except for him and Takeru. When the cloud Myotismon created left central Tokyo helpless and out of communication, Jou took Takeru to enter the main area. Unfortunately, they were attacked, and Gomamon digivolved into his champion, Zudomon and helped them have safe passage to the downtown core.
Before they left off to the final battle, Shin was able to talk to Jou. He told Jou that he didn't have to become a doctor if he didn't want to and that he should make choices for himself now. Shin had absolute faith in his younger brother.
The Dark Masters Saga was a mess. The group decided to split; Matt by himself while Takeri, Hikari, Sora and Taichi went on against the Dark Masters. Mimi gave up on fighting and Jou...well, he decided to stay behind with Mimi. But then, Jou got sorta confused and went off by himself. :-( Apparently, he didn't really believe in his crest anymore; that whenever you needed something, Jou was there, Jou the reliable. He had that point when he didn't know why he was chosen and what he was doing in the digiworld in the first place . But he mustered up some courage and helped Yamato try to get Sora out of her tunnel of darkness. They returned home, safe and sound, and Jou returned back to school with a whole new attitude. ^_^
In the fifth episode of the new season, "Old Reliable" Jou returns to save Gomamon and help the new digidestineds destroy another black spire tower. He's almost a doctor and still brings supplies to the digiworld, just in case. ^_^ He nurses Iori after he was thrown into an icy river and explains to him about his experience with the digiworld (he's so much more mature now than he was three years earlier). He says everyone has a reason for being in the digiworld, including himself. ^_^
In "20 000 Digi-leagues Under the Sea", Iori lied to the office so he can get Jou out of class to help them. Jou reverted back to his pessimistic and funny guy we all loved and was able to help save the digidestined and explained to Iori about the art of lying. It's clear that his father is still alive and that he was really worried about him.
Jou returned to the scene during Christmas time when all of the digidestined---new and old---had to send digimon from around the world back to the digital world. Jou was with Iori and they went to the "Down Under" of Australia. It appears that he's still a bit queasy with water but he was a great help with Iori.
After that, Jou barely says a few words at the end of the series.