The readers are obviously more satisfied with this turn of events, as it builds up on all the hints we already had about Aoyama being the traitor, and does not bank on just a Quirk factor like it did with Hagakure. So, what major hints did mangaka Horikoshi Kohei divulge?
All major hints of Aoyama Yuga being the U.A. Traitor leading up to his reveal in My Hero Academia chapter 336
1) Aoyama Yuga is missing during USJ arc
During the villain attacks in USJ, Aoyama is missing. His whereabouts and actions aren't revealed, he does not engage in any of the chief conflicts, and doesn’t show up at the final battle against Shigaraki Tomura.
This can be interpreted as Aoyama’s first big act as the mole.
2) Forest training arc
Horikoshi gave us several hints regarding Aoyama being the traitor during the Forest Training arc.
Aoyama Yuga’s quirk training
His quirk training was repeatedly firing his navel laser to build up endurance. Present mic’s concern was that the mole had shared their location with the league of villains in secret, but Aoyama’s laser works as a beacon that can be seen from far away.
This can be seen in the Pro-Hero License Exam arc. With him firing it repeatedly, the villains did not need an exact location.
Aoyama Yuga is missing on the map
Aoyama Yuga is missing on the map that shows the location of the students during the villain attack. A similar instance with him being away from his bed as well.
Dabi spots Aoyama Yuga but does not attack
Aoyama Yuga is later revealed to have been paired with Yaoyorozu for the test of courage. The latter had left him with a gas mask and their unconscious classmates, Hagakure and Jirou.
Aoyama hides behind a bush as Dabi and Twice arrive. Dabi suspects someone is hiding behind the bush and moves towards it, but is later stopped by Twice. Whether Dabi leaves due to The Nomu crisis, or because he recognized Aoyama as an ally, is left unclear.
Aoyama Yuga was against class 1-a going to rescue Bakugou
Aoyama, like most of class 1-a, is against rescuing Bakugou during the hideout raid arc. When Midoriya, Todoroki, Kirishima, Iida, and Yaoyorozu leave to rescue Bakugou on their own, Aoyama is unaware of it, and thus could not alert the villains about it. He later watched All Might battle AFO with a relative.
3) Aoyama Yuga stalks Midoriya
It is during chapter 167 that we get the biggest hints of Aoyama being the traitor. He behaves weirdly with Midoriya, showing up at his window later at night and leaving a message with cheese crumbs that reads:
“I know everything.”
Later, he tells Midoriya that similar to him, his quirk is also incompatible with his body. A brief flashback shows Aoyama confessing that he doesn’t want to be different from everyone else. He later told Midoriya that he had had to wear his belt for most of his life to prevent his quirk from harming him.
Now that it has been revealed that Aoyama Yuga was handed his quirk by AFO, his understanding of Midoriya makes sense. But while Aoyama may have been trying to get closer to Midoriya in order to acquire information, we now know that the latter is not the U.A. traitor by choice. Interestingly, he may have genuinely empathized with Midoriya.
Aoyama Yuga is the only one to see Midoriya awaken Blackwhip
Aoyama, because he lives directly under Midoriya’s room in Height Alliance, was the only one who woke up when the latter awakened Blackwhip in his sleep. He comes to investigate and sees Midoriya’s glowing hand with his room being in disarray.
Aoyama probably did not understand the significance of this incident, but he would have passed the information onto AFO or Dr Garaki nonetheless. Interestingly, this coincides with Gigantomachia’s awakening and Shigaraki’s consequent development at the hands of Dr Garaki.
4) Aoyama Yuga was absent during Midoriya retrieval
Aoyama knows nothing about the mountain villa or the hospital raids until the very last moment, which is why it makes sense that he could not warn the villains. When class 1-a goes to retrieve Midoriya during the Tartarus Escapee arc, Aoyama is largely inconsequential.
Given the rapport he had previously built with Midoriya, it seems weird that Aoyama would not take a more active role. This is what ultimately prompts Hagakure to spy on him.
There were many more little hints and clues about Aoyama Yuga’s status as the U.A. traitor. However, with Horikoshi shocking the readers on every chapter, it would be better to keep an open mind, and wait for the official scans of My Hero Academia chapter 336. The scans are set to be released on 5 December 2021.