Something I find really interesting about BNHA/MHA is how Hirokoshi takes common ideas/tropes and changes them drastically with a single unique detail.
For example: Superheroes. Super common. But what if they were ranked? What if their income and perceived value was based on this ranking? This system gives rise to people like Enji and Katsuki, who have to be the quantifiable best. In a sense, I think it gives these otherwise uninspired people a purpose. For early Katsuki and Enji, it wasn't about the saving. It was about the score. The win. Beyond the egoists, that ranking system has quite a few other repercussions. All Might and how Japan became dependent on him is another deep topic.
The ranking system pops up in quite a bit of the MHA fic I've read; it seems as though many fans buy into the idea of the ranking system being meaningful and adding intrinsic worth. There's a kind of tip-toeing around the fact that Izuku is obviously stronger than Katsuki at this point. But because Katsuki wants it more than anything...
Another twist on a common superhero trope: The whole concept of heroes living as accessible celebrities, and not necessarily deigning to be that, but pursuing that because it helps their rankings... it's very interesting and very clever.
