Honestly, conflict in Piccolo x Reader fics kinda follows a formula, but the specifics depend on which version of Piccolo you're writing. If it's early 'Z' Piccolo, you're usually dealing with that whole 'I'm a demon king's son, I'm not supposed to care about anyone' thing clashing with the reader character somehow getting under his skin. It's classic 'loner vs. connection' stuff. The conflict is almost entirely internal for him, which makes for some great angsty introspection if it's done well, but can also get repetitive if every story is just him brooding on a cliffside for 20 chapters.
Then there's the more common post-Namek fusion Piccolo, where the conflicts get way more interesting, I think. He's still gruff and alien in his thinking, but he's also Got into the mix now, so there's this weird softness warring with his natural pragmatism. A lot of stories use the reader being a human as the main hurdle—his lifespan is centuries longer, his power level means he perceives danger completely differently, and his cultural references are nonexistent. I've seen some clever fics where the reader is a scientist or a historian trying to document Namekian biology or culture, and the conflict comes from Piccolo being intensely private versus their academic curiosity, which feels way fresher than another 'I can't love you, it's a weakness' plot.
My personal favorite conflict theme, though, is when the reader is another fighter, maybe not Saiyan-level but competent. The tension there isn't about fragility, but about philosophy. Piccolo's a strategic, ruthless warrior at heart; the reader might have a more heroic, protect-the-innocent code. Watching them argue over the 'right' way to handle a threat, with Piccolo advocating for the efficient, permanent solution and the reader holding out for mercy, creates a fantastic dynamic that tests their bond without making either character seem dumb or overly emotional. It respects both their intelligence. I just finished one where the reader was a former Red Ribbon android, and Piccolo's distrust of her tech origins versus her proving her autonomy was the core tension, and it was brilliantly executed.