I'm not sure specifically what 'Cap deage' means. It could be a very specific term, a misspelling, or something relatively unknown. It might be a proper name, a local term in a certain area or a very niche concept.
The cap man and monkey story is an interesting one. There was this cap man who was traveling around selling his caps. He reached a place near a forest and decided to take a rest under a tree. While he was sleeping, the monkeys in the tree noticed the caps. They climbed down, grabbed the caps, and went back up the tree. When the man woke up, he was confused at first, then saw the monkeys with his caps. He was worried as those caps were his livelihood. But then he remembered that monkeys often mimic human actions. So he took off his own cap and tossed it. The monkeys, being the imitators they are, did the same with the caps they had taken, and the cap man got his caps back.
There probably is. Many fans create their own interpretations in fanfiction. Naruto and Kenichi are both popular series, so it's not uncommon for someone to combine them in a 'godlike' scenario. However, the quality and availability might vary. Some fanfictions could be really well - written, while others might not be so great. It really depends on the creativity and writing skills of the individual authors.
Another theme is the OC's role in the conflict within the Kenichi world. Whether it's helping Kenichi and his friends fight against a new enemy or getting involved in internal disputes among different martial arts groups. This theme shows how the OC can impact the pre - existing story structure and bring new twists to the narrative.
One popular 'kenichi fanfic' could be 'Kenichi's New Adventure' which might explore new martial arts challenges for Kenichi. Another could be 'Kenichi and the Mysterious Ally' where he teams up with an unexpected character. There are also some fanfics that focus on Kenichi's relationships, like 'Kenichi's Growing Bonds' which delves into his friendships and how they evolve over time.
Often, they highlight the contrast between Kenichi's more naive and determined nature and Shigure's more experienced and mysterious side. Their love is shown as something that bridges these differences.