Fan Works / Missed The Call

In Amazing Fantasy, All Might muses that Izuku could have been his successor if they had just met a few days earlier, but dispels the thought before Izuku catches onto anything.
In the Buffy the Vampire Slayer/Angel/The Hunger Games crossover Demon’s Games, once Angel’s resistance retrieve the Slayer Scythe, rescue Willow and essentially resurrect Buffy, they are able to use the Scythe to activate new Slayers from among past Victors, as they realise that the Reapings were intended to eliminate any Potentials in the Districts to ensure that no new Slayers could arise. However, Willow and Angel each make a choice not to inform Annie Cresta or Enoboria of their possible status as Slayers as they recognise that the two women have too many issues to properly deal with the responsibilities of the role.
In one My Huntsman Academia sidestory, Ozpin muses that Izuku's tactical brilliance and academic insight could have made him a perfect heir to his role as the head of The Conspiracy to protect Remnant if Toshinori hadn't swept him up first. Toshinori dismisses this, saying that Izuku's Chronic Hero Syndrome would prevent him from taking up a role as The Chessmaster.

In Game Theory Nanoha's mother Momoko has significant magical talent, but because she grew up on Earth, where there's no knowledge of magic, she never got a chance to use it. Although that's changed recently.

Alya and the Harem Reality, Master Fu, before fighting and dying against his ancient enemy, hid the Miraculous around Paris, each in a location that coincidentally was connected to their original canon holder. However this doesn't mean only they can find them: Oxtoppable found the Ox Miraculous instead of Ivan. And despite being hidden at the pool he frequents Kim did not find the Monkey, which was instead found by Lila on a chance visit.
Scarlet Lady begins when Master Fu slips the Ladybug Earrings into Marinette's purse instead of putting them in her room. Chloé then steals the Miraculous, mistaking it for a family heirloom that Marinette will get into trouble for losing... only to find herself saddled with the responsibility of becoming a heroine instead. Hilarity Ensues, especially as Chloé decides this was meant to be her destiny all along, despite being repeatedly told that she wasn't the intended bearer. Eventually, Chloé proves to be so incompetent that Fu gives Marinette another chance; as he can't get the Ladybug Miraculous back, he instead gives her the Bee Miraculous.

Live a Hero; All Might meets Izuku and thinks he'll become a great hero, but due to extensive Domestic Abuse from All For One Izuku is too mentally and physically frail to inherit One For All. All Might instead contacts Aizawa to mentor Izuku and prepare him for U.A. while providing as much support as possible, and eventually chooses Kirishima to be his successor.

Breaking (all the) Things starts with a time-displaced Akechi instinctively punching Shido in the face, turning his wrath away from Akira and preventing him from both ending up in Tokyo with a criminal record and becoming the leader of the Phantom Thieves.
The premise of It's Just a Light Rain (But the Storm's Still Comin') is that Akira grabs an umbrella as he's heading out the door for his first day at Shujin, never meets and befriends Ryuji, and never ends up in the Metaverse.

In Pokémon Reset Bloodlines, at the beginning of the story, Arceus decides not to tell Ash that he chose him to save the world because he couldn't save Cynthia and Lance before the reality collapsed in itself.

Missed The Call / Fan Works