A search for Mineta and Deku stories with school life at the core will definitely take you into some niche corners of fan spaces. I've found that the most straightforward path is to use specific tags on major fanfiction archives. On Archive of Our Own, you'd want to combine the pairing tag 'Midoriya Izuku/Minorou Mineta' with additional tags like 'UA Academy', 'School Life', 'Class 1-A', and 'Canon-Typical School Setting'. That last one is particularly useful because it filters out stories that immediately jump into hero agency or post-graduation scenarios, keeping the focus on dorm life, classroom shenanigans, and school festivals. I'd also recommend adding the 'Alternate Universe - School' tag to your search, as some writers use that to explore variations of their academic dynamic without the pressure of the hero curriculum.
Sometimes, the most dedicated content for less mainstream pairings pops up on dedicated forum threads or smaller, fandom-specific writing communities. Places like SpaceBattles or Sufficient Velocity occasionally have 'My Hero Academia' idea threads where someone might have written a snippet focusing on that dynamic, often buried within a larger discussion. Tumblr can be another source, though it requires more digging; searching the '#bnha fic' or '#mha fanfiction' tags alongside the characters' names might surface a standalone piece or a reblogged link to a story hosted elsewhere. The key is persistence and a willingness to sift through results, as these stories aren't always the most prominently featured.
The tone of these fics can vary wildly, which is part of the appeal for some readers. I've seen some that treat the pairing with a surprising amount of sincerity, building a slow, awkward friendship at UA that eventually develops into something more, using the structured environment of classes and shared dormitory life as a natural catalyst. Others lean fully into crack territory, amplifying Mineta's antics and Deku's exasperated reactions for pure comedic effect within school settings—think study sessions gone horribly wrong or collaborative projects that descend into chaos. Finding what resonates with you is a matter of sampling a few and checking the author's additional tags for tone indicators. I usually bookmark the authors who handle that specific character interplay in a way I enjoy, as they often revisit similar themes.