One interesting plotline could be Deku having to face off against his classmates in a series of challenges that test not only their quirks but also their teamwork and strategic thinking. Maybe there's a misunderstanding that leads to the conflict.
Deku himself is likely to shine. Given his powerful quirk and his growth throughout the main series, he'll surely put up a great fight against his classmates. Bakugo could also shine as he's always been in competition with Deku and has a very strong quirk.
One interesting aspect could be the different interpretations of the characters' powers. In fanfiction, the author might explore new ways Deku uses his One for All ability against Overhaul's powers. It can also show different battle strategies that might not be in the original manga or anime.
You can try looking on fanfiction websites like Archive of Our Own (AO3) or FanFiction.net. These platforms usually have a wide variety of fanfictions, including ones related to 'Deku vs Overhaul'. Just use their search functions to find what you're looking for.
I really like 'A New Alliance'. In this fanfic, Momo and Lemillion team up to create a new training regime for the students at UA. It delves into their different quirks and how they can complement each other in a training environment. There are some really cool action scenes as they test out their new training ideas on each other.
One popular trope is the 'Mentor - Mentee' relationship. Sometimes, Lemillion is written as a mentor to Momo, teaching her how to be more confident in using her quirk in combat situations. Another is the 'Partnership' trope, where they team up for various missions and grow closer as friends and comrades.