The dragon gives off an air of intimidation and fear when first introduced and even tried to kill Jack before his stomach started acting up, and was likely simply fighting in self defense. When Jack offered to aid it, the dragon was far more welcoming.
The dragon has an offspring: the Baby Dragon.
During his journey, Jack came upon a ravaged village full of people and animals near death. As he was getting near the village, he smelled the most awful stench imaginable. While traveling through the village to see what was causing the whole problem, he met a man with no nose who told him of a dragon that lives on a mountain close to the village, and that the smell was coming from there. Jack travelled up the mountain, past a massive cloud of stink, and made it to the dragon. The dragon at first tried torching the young samurai, even coming close to killing Jack, but gave up when his stomach pains returned and let out a large blast of gas. The dragon revealed that he has been farting more than usual lately. He originally felt great releasing his gas and feeling immense relief, at the hands of the villagers, but it eventually led to stomach pains that grew. The dragon then persuaded Jack to enter his body to find out what was causing his pain. Realizing the dragon was only harming the villagers by proxy than intent, the samurai reluctantly agrees. After traveling through several organs and fighting off strange antibodies and bacteria, Jack discovered the cause; it was a baby dragon that was breathing fire on the Dragon's organs (odd as the dragon seemed to be male). Jack then grabbed the egg and managed to make it out before another blast and saved the village from the Dragon's flatulence. Unfortunately, the baby dragon was trigger happy and began breathing so much fire that the entire village caught ablaze just as Jack was about to leave.
It is unknown how the past Aku's destruction affects his existence.
- The Dragon having a baby inside it would mean the Dragon is female with a very deep voice, or it is a male and reproduced its baby asexually. In the case of the latter, this is among the few instances where male-pregnancy is portrayed in a children's cartoon.
- The Dragon seems to be massively larger on the inside compared to its elephant-sized outside, with the change noticeable as soon as Jack enters its mouth. The reason for this is unknown.