My Hero Academia fans have countless theories about Izuku Midoriya's Quirkless nature, with plenty determined to somehow "give" Deku his natural Quirk factor back. Being born truly Quirkless is a source of stigma and shame in this world, so some fans have decided that Dr. Garaki is responsible for the protagonist's unfortunate state.
Many want to make Garaki, All For One's assistant, the bad guy who stole Deku's natural Quirk factor so there's a clear villain to blame for his Quirkless state in childhood. It's an intriguing fan theory that's meant to defend Deku, who couldn't help having his Quirk stolen. However, in this case there's strong evidence in the story that Dr. Garaki is fully innocent.
The MHA Fan Theory of Deku's Stolen Quirk Factor
Some My Hero Academia fans insist Midoriya really was born with a natural Quirk factor, but that Dr. Garaki, who was his pediatrician at the time, took this opportunity to steal it. He is, of course, also All For One's insidious scientist ally and sidekick, promoting villainy by blending Quirks and dark science to create the monstrous Nomu. Being a legitimate pediatrician would allow Garaki to assess many children's Quirks up close, then choose some to steal for All For One. The fan theory says he did just that to Midoriya and lied about the boy being born totally Quirkless.
There are a few reasons to promote this theory. If Dr. Garaki, of all people, is Deku's pediatrician, then he must play a bigger, more villainous role in the boy's character arc. It would seem silly for an important scientist villain like Dr. Garaki to just make an innocent cameo and nothing more. This plays into the "Chekhov's Gun" literary theory, that anyone or anything interesting that appears must be important, otherwise there's no reason to include it.
Another possibility is that MHA fans simply feel sorry for the young, Quirkless Deku in those flashbacks, so they "gave" his Quirk back so Deku wouldn't endure the unfortunate social stigma. If Dr. Garaki sneakily stole Deku's natural Quirk factor, then it's solely his fault that the protagonist grew up an outcast, and fans can focus all their anger on one person. This paints the Midoriya family as an innocent victim of a villain who's easy to blame for all of Deku's early troubles.
Dr. Garaki Couldn't Steal Any Children's Quirks While at Work
This My Hero Academia fan theory is intriguing and gives Dr. Garaki a fascinating subplot, but most evidence in the anime contradicts the idea of Deku's stolen Quirk factor. Garaki may be All For One's sidekick who experiments with Quirks in ingenious ways, but he's no Quirk thief. It's the opposite -- rather than taking them away, he duplicates people's Quirks and gives them to the likes of Tomura Shigaraki and the various Nomu. Garaki lacks the Quirks or scientific equipment necessary to outright steal Quirk factors from children like Izuku Midoriya. It's All For One who steals Quirks, and even he cannot do it remotely -- he must touch the other person to claim their Quirk.
Also, Dr. Garaki stands to gain little from stealing most Quirks even if he could. Aside from powerhouses like Shoto Todoroki and Katsuki Bakugo, many children have unremarkable Quirks not worth stealing for the League of Villains' cause, even with the Quirk Singularity approaching. Given Inko's minimal Quirk and her husband's unremarkable Fire-Breathing Quirk, it seems unlikely that Deku inherited anything All For One or Dr. Garaki would bother stealing.
Most of all, Dr. Garaki would soon be caught and arrested if he were somehow stealing Quirks from his patients at his job as a pediatrician. Even if he chose just one child to steal a Quirk from to avoid suspicion, the chances seem incredibly remote that Deku, of all people, had a Quirk worth stealing. Ultimately, even if MHA fans want to make Dr. Garaki's subplot more interesting with this theory and comfort Deku by imagining him being born with a Quirk, there's no clear sign that any of this did or could have happened. Dr. Garaki has committed many crimes for All For One's cause, but stealing Quirks from kids isn't one of them.