Well, in the 'king piccolo meets his son' fanfiction, it could be that the son has some sort of special ability that King Piccolo wants to use for his own evil purposes. However, the son resists. There could also be a sub - plot where other characters from the original story get involved. For example, some of the good guys might try to protect the son from King Piccolo's clutches. And in the end, the son might either change his father for the better or have to defeat him to save the world.
The relationship could start off very rocky. King Piccolo is used to being in control and his son might be more independent - minded. But over time, they could develop a grudging respect for each other. For instance, if the son shows great strength in combat, King Piccolo might start to see him as an equal.
I haven't actually read this specific 'piccolo and gohan lemon fanfiction', but generally, in fanfictions involving these two characters, it might explore their relationship in unique ways. It could be about their friendship evolving, or perhaps their teamwork in new and unimagined scenarios within the Dragon Ball universe.
A major theme is identity. Since she is a female version of Piccolo, she has to come to terms with who she is compared to the original Piccolo. Family also plays a role. In some fanfictions, she might be searching for her family or creating a new family of her own. Additionally, the theme of good vs. evil is common, as she battles against various villains.
I'm not that familiar with the specific 'Brian Piccolo Thanksgiving Day story'. Maybe it could be about how he spent the Thanksgiving Day with his family, sharing a big meal and giving thanks. It might also involve some special traditions he had on that day.
I'm not entirely sure which specific 'piccolo x gohan lemon fanfic' you're referring to. But generally, if it's a fan - made story, it might explore unique relationships and character developments. It could potentially show how Piccolo and Gohan interact in a different way than in the original series, perhaps delving into their friendship or a more complex emotional bond.