WARNING: The following contains spoilers for My Hero Academia Season 5, Episode 19, "More of a Hero Than Anyone," now streaming on Funimation, Hulu, and Crunchyroll.
Tomura Shigaraki has been largely absent from Season 5 of My Hero Academia, with only an occasional glimpse at whatever wildness he's up to offscreen. At the very end of Season 5, Episode 19, Shigaraki appears once again, this time undergoing some sort of experiment or possibly even straight-up torture. The mysterious man seen conducting the procedure makes it sound as though Shigaraki is about to make his grand return, new and improved.
The doctor overseeing the procedure only has a few lines of dialogue, but they are quite revealing. He clearly does not work for Shigaraki, considering he refers to the boy as the masterpiece he and All For One have been searching for, a being of ego and unlimited power. While Tomura's Quirk is no laughing matter, it's never been shown to be "unlimited," indicating this experiment may result in it becoming dangerously stronger.
The fact that this doctor is clearly All For One's subordinate, as well as the indication this is part of All For One's plan, does not bode well for Shigaraki. The sheer violence of this experiment and Tomura's suffering make it clear he is still nothing more than a pawn to All For One. While Shigaraki likely stands to benefit from this torture, its full purpose pertaining to All For One's desires may not be revealed for quite some time.
Interestingly, the preview for the following episode may contain a major clue about what is happening to Shigaraki. Gigantomachia, All For One's former bodyguard, is said to be testing Tomura to see if he is worthy of being a successor. Given the similarities between All For One and One For All, the word "successor" hardly seems like a coincidence. It's possible My Hero Academia is gearing up for Shigaraki to inherit the Quirk of All For One.
That said, it sounds completely out of character to suggest All For One would ever give up his power, so the true purpose of Shigaraki's experiment could be anything at this point. Considering Season 5, Episode 20 will be a flashback episode addressing what the League of Villains has been up to, fans may not have to wait too long for an explanation. It's been a while since the League was in the spotlight, so it will be interesting to spend some extra time with the notorious criminals.
My Hero Academia fans were confused when Season 5 skipped an entire arc from the manga. However, the preview for Season 5, Episode 20 reveals that the famous My Villain Academia storyline wasn't skipped, just pushed back. This missing arc resulted in Shigaraki's extended absence from the series, though he appears poised to take on a central role for the back end of this season. Despite all the uncertainty, one thing's for sure: when Shigaraki returns, he's going to be a bigger menace than ever before.