One acceptable theme is their relationship in terms of power balance. How Piccolo's different forms compare to Cell's various stages of evolution. Also, the psychological aspect of their encounters, like how they perceive each other as opponents, can be a great theme for fanfiction.
Writing such fanfiction that involves inappropriate and non - canon sexual content is not appropriate. Dragon Ball series is mainly focused on action, adventure, and the development of characters and their powers, not this kind of vulgar content.
When facing a common enemy, Naruto's Nine - Tails chakra could be combined with Alucard's vampiric powers. For instance, the Nine - Tails' massive chakra could fuel Alucard's more energy - consuming abilities, such as his ability to summon a large number of familiars. In return, Alucard could use his knowledge of dark magic (if in the fanfiction) to help Naruto better control the Nine - Tails' chakra, maybe even creating a new form of chakra - powered attack that combines both of their unique natures. This combination would be extremely difficult for the enemy to counter, as it would be a blend of two very different and powerful power sources.
In a Tournament of Power fanfic, Cell's performance against other competitors would be complex. Against those with lower power levels, he would be a terrifying presence. He could use his various forms and techniques to overpower them. But as he faces stronger adversaries, things get tricky. His strength is significant, but compared to the top - tier fighters like Toppo or Hit, he might struggle. His best bet would be to use his cunning. For instance, he could try to create chaos among the enemy ranks, making them fight each other before engaging in direct combat himself. This way, he could conserve his energy and pick off the weakened foes.
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.
I recommend "From the Death row", which is a fantasy novel about a different world. The female protagonist, Wang Zhongping, woke up to find herself in a cell, and the male protagonist was also in it. The plot was set up with a hidden mystery, and the development of the plot was compact and exciting. It was very worth watching. I hope you like this fairy's recommendation. Muah ~😗
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.