Izuku Midoriya's actions don't always match his personality. Deku is one of My Hero Academia's most promising Pro-Heroes in training who excels at strategizing. Deku is highly calculating and can memorize the Quirks of heroes and villains alike in precise detail.
As a teammate, Deku doesn't hesitate to lend a helping hand to his allies and risk his life to ensure their safety in the end. To become the legendary hero he wants to be, Deku is prepared to master his Quirk's abilities using whatever means necessary. However, the burden of being One For All's inheritor influences his actions in unexpected ways.
Warning: manga spoilers ahead.
10 Deku Left His Dream School, U.A.
During the Paranormal Liberation War Arc, Deku willingly leaves U.A. after learning horrifying secrets about One For All. Attending U.A. has always been Deku's greatest dream, and everything he's worked for has been to graduate as a Pro Hero. Deku suddenly abandoned the lifelong plan he had for his future.
By leaving U.A., Deku also isolated himself from his classmates. Up until he left, Deku has always been the type of person to support his friends with his physical presence, such as when he helped subdue Stain. His sudden decision to distance himself entirely opposes his usual demeanor towards his fellow classmates.
9 Deku Agreed To Fight Bakugo
Deku frequently endures Bakugo's taunting, and although Deku makes his rivalry with Bakugo clear, his general reaction to Bakugo's hostility is apologetic and timid in nature. Deku pointedly avoids direct confrontations with Bakugo outside of U.A. training, yet after Bakugo ordered Deku to fight him after learning One For All's secret, Deku abandoned his usual reluctance and accepted.
Although Deku agreed to fight out of genuine concern, he willingly chose violence as a means of addressing his past with Bakugo. Up until this moment, Deku largely sought to pacify Bakugo's rage rather than acknowledge it through battle.
8 Deku Altered How He Uses His Quirk
Deku has commonly relied on his arms to use his Quirk. However, One For All's power damages Deku's body when used recklessly. Rather than limiting himself, Deku habitually injured his arms to surpass his Quirk's capabilities. After months of ignoring severe damage, Deku abandoned his flawed technique for the leg attacks of Shoot Style.
As All Might is Deku's hero, Deku has tended to imitate All Might's fighting style despite his comparatively weaker strength. By altering how he uses his Quirk to suit his own body, Deku changed his initial idea of how to handle One For All.
7 Deku Criticized All Might
Deku considers All Might the ultimate role model for heroes and frequently turns to him for advice on his Quirk. Although Deku greatly respects him, there have been times when Deku was unusually critical of All Might. When Deku discovered that All Might was hiding Nighteye's disapproval of One For All's successor, Deku admonished All Might for keeping secrets from him.
Deku was once again critical of All Might's decision making when he learned that All Might had hidden Nighteye's prediction of his death. When All Might isn't honest with him, Deku loses part of the trust he normally holds for his role model.
6 Deku Refused His Friends' Help
Deku trusts his classmates and willingly works with them in crises, such as when he collaborates with Iida, Kirishima, and Shoto to rescue Bakugo from All For One. However, after Deku runs away and his classmates plead for him not to face All For One alone, Deku refuses to accept their help and resists.
While suffering from the expectations of being One For All's successor, Deku stops seeing himself as a person with supportive allies despite his friends' best efforts to convince him otherwise. Deku uncharacteristically places himself in the role of a lone fighter who faces evil alone.
5 Deku Injured Uraraka With His Quirk
Deku and Uraraka share a close friendship and always protect each other from harm. Even when they had just met, Deku saved Uraraka from being crushed during the U.A. Entrance Exam. However, after Deku's Blackwhip Quirk manifested during Class 1-A and 1-B's joint combat training, Deku injured Uraraka after she attempted to call him down.
Although Deku injured Uraraka unintentionally, it was the first time that Deku caused her direct harm and failed to regain control. Deku always works to shield his friends and civilians from One For All's power, but he occasionally fails to protect them completely.
4 Deku Left Eri In Overhaul's Care
Deku immediately acts to save people in trouble, as seen when he instantly attacked the slime Villain who was slowly killing Bakugo. If it's possible for Deku to save someone, he doesn't leave until he finds a way to do so. However, Deku abandoned that principle temporarily when he let Eri leave with Overhaul after recognizing she was fleeing from him.
Deku passed the opportunity to save someone who was desperate for help, though the choice to do so took all of his willpower. To his regret, Deku put a future plan before a victim's safety.
3 Deku Let Shigaraki Walk Away
Deku doesn't let Villains walk away unchallenged, as seen when he refused to allow Gentle Criminal to disrupt the School Festival. As a reckless person, Deku is unafraid to challenge villains who outmatch him to protect someone, such as when he saves Kota from Muscular. However, Deku let Shigaraki escape after he forcibly interrogated Deku in the mall.
Since Shigaraki threatened to attack civilians if Deku resisted, Deku held back his usual instinct to fight and protected those around him with non-violence. When Shigaraki left, Deku made no move to pursue despite the danger Shigaraki posed to society.
2 Deku Told Bakugo The Truth About His Quirk
After receiving One For All from All Might, Deku promised to hide that he was All Might's successor. Deku denied any comparisons his classmates drew between him and All Might and pretended his Quirk was always his. However, Deku broke his promise to All Might and admitted to Bakugo that his Quirk came from somebody else.
Deku's hint to Bakugo about his Quirk's origins was enough for Bakugo to realize that Deku was All Might's successor. Rather than denying Bakugo's accusations as he would to anybody else, Deku allowed him to be an exception.
1 Deku Misjudged Gran Torino
Deku trusts All Might's judgment regarding his training and seeks his opinion on where to do his hero internship. After All Might recommended Gran Torino, Deku was initially enthusiastic about learning from a hero who All Might respected. However, after witnessing Gran Torino's eccentric behavior, Deku doubted All Might's advice and judged Gran Torino as incompetent.
To Deku's surprise, Gran Torino turned out to be testing Deku and quickly pointed out the flaws in Deku's fighting style. Deku thought that All Might made a mistake in his choice of proper teachers, despite Deku's usual trust in All Might's advice.