I was watching the movie Heros Rising and while they were describing how Nine got his quirk it briefly shows "The Doctor". He explains to Nine that he has All for One's quirk, which means he can have nine quirks as well as his own. It's never explained how this works, so I was wondering if anyone caught onto it and look into it more. My only theory is that All for One is just like One for All, where it can be transferred, but that is immediately shut down because the movie has almost connected to the show itself. After all, it would affect the storyline too much. If someone could explain, it would be appreciated.
He gained it through the experiment
he became the test subject of Dr. Daruma Ujiko's experiment, which granted him the Quirk known as All For One, allowing to steal and use up to nine different Quirks.
This is on Wikia,
The doctor is a mad scientist who experiments on people frequently. Not much is really known other than this and it might be explained more in the future as we know that Shigaraki will inherit All For One's power. And has already started to
Tomura's second Quirk is the original version of All For One used by his master. It allows him to steal other people's Quirks and use them as his own. All For One's first user intended to have Tomura inherit his Quirk
This is both here:
Perhaps it's given to Nine the same way as a test to see how it could be transferred to Shigaraki. It's complicated but it seems like All for One can definitely be transferred in a way just like One for All just Maybe not by DNA unless it's a different form of DNA such as blood possibly. We don't know what happened during the experiment so I can't say for sure whether blood transfusion was a part of the process or not but it may very well be. Hope this helps.