In many BNHA fanfictions where Izuku meets All Might early, it often changes the entire trajectory of Izuku's development. For example, he might gain confidence much sooner. Early meetings can also lead to a more in - depth mentorship that might deviate from the original storyline. This could result in Izuku getting special training earlier and potentially unlocking his Quirk in a different way.
One consequence could be a faster growth in Izuku's power. With All Might's early guidance, Izuku may master his Quirk more quickly. Another is that his relationships with other characters might change. For example, Bakugo could become more jealous or, on the contrary, might be inspired to work harder.
A cool plot might be that the BNHA villains discover the Dream SMP and see it as a new place to expand their evil plans. They kidnap some of the SMP members thinking they can use them for something. The SMP members then team up with the BNHA heroes to fight back. Techno could use his combat skills and the BNHA heroes would be amazed at his fighting style without having a Quirk. And the SMP members could learn about the importance of working as a team like the BNHA heroes do.
Well, perhaps in this fanfiction, the quirks in the BNHA world start to have an unexpected effect on the Afton family. Freddy Fazbear could gain a quirk that makes him able to control people's minds, similar to some of the mind - control quirks in BNHA. The Afton family then uses this newfound power to try and create chaos in the BNHA world. And the BNHA characters have to figure out how to stop them while also dealing with their own internal conflicts and challenges.
Nezuko is initially 12 years old in the manga. As the story unfolds, her age doesn't change significantly in a traditional sense, but her character development is quite remarkable.