You know, most folks default to the 'For Want of a Nail' thing—Izuku gets One for All a year early at I-Island, and Melissa builds him a prototype support gear. The central tension then becomes whether he still needs the quirk, or if she can engineer a path to heroism for him without it. It’s essentially a power fantasy with a side of imposter syndrome; he’s terrified he’s cheating or taking a shortcut, while she’s overworking herself to prove the tech is valid. I’ve seen a few where he never gets the quirk at all, and the entire plot hinges on Melissa’s inventions failing spectacularly at critical moments, forcing them to rely on pure, quirkless strategy. That can be pretty gripping if the author remembers that failure needs consequences.
Another huge one is the mentor/protégé dynamic flipped on its head. Melissa, as David Shield’s daughter, has this immense legacy pressure, and Izuku, the fanboy, looks up to her technical genius. The conflict comes from them trying to live up to each other’s unrealistic expectations. She thinks he’s the 'real' hero, he thinks she’s the brilliant one, and they both spiral trying to be worthy. It gets melodramatic fast, but the core is relatable. There’s also the occasional 'All Might is Disappointed' subplot, where Toshinori feels his successor is abandoning the legacy for gadgets, which adds a nice layer of generational angst.
Honestly, the most interesting fics to me are the rare ones that ditch the hero academy setting entirely. They meet as interns at I-Island, and the central conflict is corporate espionage or an ethical dilemma about quirk-suppressing technology. The romance becomes a slow burn built on shared moral compasses clashing with practical necessities. It’s less about flashy fights and more about two smart kids in over their heads, which I find way more compelling than another UA retread.