The wicked All for One has made his move on Tomura Shigaraki in the main series, but My Hero Academia Vigilantes indicates he had some practice first.
In recent chapters, the past of Vigilantes’ primary villain, Number Six, has been explored, depicting how as a boy, he was experimented on by All for One and his minion Dr. Garaki. It’s been known for a long that All for One’s Nomu are formed from ordinary individuals, frequently ones who’ve just died, which may be the situation for Six.
All for One presented him with a quirk, and carefully conditioned the youngster to imagine the quirk’s previous owner, O’Clock, in his head, imparting counsel. While Six has picked up many additional quirks in the decades afterwards, the O’Clock quirk is still his major interest, and that phantom hero has repeatedly emerged throughout Vigilantes.
Fans have theorized for quite some time now whether this O’Clock in Six’s mind is a hallucination, or a residue of the quirk’s former users, akin to One for All.
In Chapter 113, however, it’s become evident that the reality is more complicated: the incorporeal O’Clock isn’t a mere remnant, but an active element of All for One that’s been studying Six’s moves. This still (somewhat) correlates with the vestiges, since it was established that All Might has some awareness of the All Might vestige that resides in One for All, but the relationship is much, much greater. A better analogy seems to be to what’s occurring with Tomura Shigaraki in the main series’ manga right now, as All for One progressively takes over Shigaraki’s body, and their consciousnesses have begun to join.
All for One himself even hints this when he speaks, referring to Six as a wonderful “Guinea Pig.” Number Six wasn’t simply an experiment at making a monster to fight for him; he was supposed to be a practice effort before All for One launched his plan to steal Shigaraki’s body.
After all, All for One had been “raising” Shigaraki since he was only five years old, and his age in the manga’s present is 21, thus there were at least 15 years before My Hero Academia began where the plan was in process, but not ready to be completed. It only seems reasonable that All for One would undertake some test runs before attempting it on Shigaraki, especially because it was so vital to him to employ this youngster in particular. In a way, that makes Six all the more terrible of a villain: he’s undergone so much misery, and it was all just preparation, planned for use on someone else. Six was always designed to be abandoned.
This also gives a little insight into a small enigma of late. While the main My Hero Academia manga has had a few unexpected breaks this year, Vigilantes is authored by a separate individual and should be unaffected. Yet, especially with this most recent hiatus, Vigilantes postponed its release as well. If the disclosures in both tales are supposed to sync up, it’d be vital to maintain the releases in rhythm. If that’s the case, there should be a few more thrilling disclosures in My Hero Academia to come.