It could mean that 'flan' is a work of fan - created fiction within the Harry Potter universe. Maybe it's a story someone wrote that uses the characters, settings, or concepts from Harry Potter.
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.
Well, you can look at the writing style. If it's engaging, with good descriptions of the magical elements and the characters, that's a plus. Also, if it adds something new and interesting to the Harry Potter universe, like a unique plot or a fresh take on a character relationship. For instance, if 'flan' has a great story about how the Marauders' Map was actually created in more detail, it could be considered good fanfiction. Another aspect is the grammar and spelling. If it's error - free, it makes the reading experience much better.
I don't have enough information to say exactly who Cap'n Kathy is. She could be an original character created by the fan fiction writer. Maybe she's a pirate - the 'cap'n' part could suggest that - who has some connection to the wizarding world of Harry Potter.
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.
Spider - Man's light - hearted and quippy personality can provide a contrast to the more serious and stoic members of Team Cap. His sense of humor can lighten the mood during tense situations. For example, in a battle, he might crack a joke to ease the tension among the team members.
One common theme is heroism. Cap Neil is often depicted as an even greater hero, facing tougher challenges and emerging victorious. Another theme could be sacrifice, showing how he would give up something for the greater good.