One interesting subcategory of fanfic is that of the For Want of a Nail story basis. Basically, keep all the canon background and characterization except for one small detail. That small Alternate Universe element can then allow for a much different outcome. A character misses a canon shot, or takes one they would have missed. Someone walks left instead of right into an ambush. A message gets through in time, or doesn’t get through at all. The same characters, the same history, the same prior events – but the ripple of that one change can affect everything.
I think of Nail fanfics as being somewhat like haiku, sonnets, bonsai, or feng shui’ing a room. You’re deliberately limiting what you can write, by trying to work within a restrained framework of what you have available (canon) and what moves you can make (the Nail). Within that framework, though, you can express a lot of creativity. Look at the DC Elseworlds comics for an official version of this, or various alternate history books, or the whole 1632 series by Eric Flint and others. That’s where a Nail of “one small Virginia coal mining town” gets pounded through time into the Germanies of the 1600s by an unknown alien race entertaining themselves with time-sculpture. No advanced science on Earth, no magic; just known historical figures, events, geology and otherwise. But everything changes for Germany and the whole world, as knowledge and altered events ripple outward.
Despite the name, though, For Want of a Nail actually comes in two main forms. You can add something to canon, or take something out. The 1632 series adds a mining town to history. Cover, a Bleach AU by glacis, takes out some of Ichigo’s straight fighting drive and switches it to “I fight so that I can still dance, which is what I want to do”. Still Ichigo, still fierce and staunchly morally upright in defense of his family, but character relationships and events shift in response to different goals.
Also remember that any For Want of a Nail bit you throw in is a starting point. Depending on how a writer spins out the ripple effects of the change, you could end up with something very close to canon, or… not. *Facepalms* See Embers. Or more accurately, see Theft Absolute, which was the Nail of Not Stealing an Ostrich-Horse. Embers… snowballed, from there. (I blame grad school. It drives one a bit crazy. Okay, maybe more than a bit.)
And if you want some more Nail example fics….
Yesterday Upon The Stair by PitViperOfDoom (BNHA)
An unsuspected Quirk leads to a different life for Izuku. Note: Horror movie levels of creepy, ghosts.
To Take Care by Haicrescendo (AtLA)
Fluff. Serious Airbison fluff.
Auxiliary by Oceanbreeze7 (Voltron: Legendary Defender)
Re-finding your (alien) family.
fear is the monster you forgot to flee from (fear is the monster that won’t let you go) by cywscross (나 혼자만 레벨업 | Solo Leveling (Webcomic)
Monster hunter comes back as something… Eldritch. I loved it, but then I love a lot of Lovecraft, so take that as a warning.
And here are three particularly awesome Mo Dao Zhu Shi Nail/canon divergence stories: Heliocentric, when you’re doing all the leaving (then it’s never your love lost), and picking up the pieces.