The following content contains spoilers from Season 6 of My Hero Academia, currently streaming on Crunchyroll. Apart from the obvious Quirk additions gifted to him by All For One and the bonus upgrades that Dr. Ujiko eagerly contributed, Shigaraki has made some severe personal developments since fans first met him in Season 1.
Deku, Bakugo, and the other Heroes aren't the only ones working on improving themselves, as Shigaraki certainly has some large shoes to fill as the Symbol of Evil's successor. While his actions are far from admirable, Shigaraki has learned to overcome his flaws to become the best Big Bad in the series and deserves to be commended for his efforts.
Its Showtime for Shigaraki
When fans first meet Shigaraki, he certainly sends out sinister and foreboding vibes; however, his anxious, almost sensitive nature comes across as rather immature, like a spoilt brat throwing a temper tantrum. All For One's prodigy shows great determination and has high aspirations, targeting the #1 Hero in his first solo mission but, as soon as things don't go according to plan, Shigarki starts to unravel at the seams. It becomes evident how heavily the young man relies on All For One's guidance, as he can often be plagued with self-doubt and second-guesses his strategic decisions, costing him dearly in the end. When his father figure is not around, Kurogiri appears to be the only one capable of calming Shigaraki when he starts to spiral and has become quite skilled at influencing the temperamental psychopath off the precipice of self-destruction.
One surefire way of evaluating Shigaraki's emotions is to assess how itchy he appears to be while taking note of the hands adorning his body. If he is relentlessly scratching or any of those creepy hands happen to be missing, it's a sign to flee because this miscreant has likely just initiated a destructive warpath. Things get even more disturbing when the audience discovers whose hands those actually are; not mere props to boost his intimidation factor, but the literal remains of Shigaraki's own family, who he murdered in cold blood when he was but a boy. Unable to control his Decay Quirk when it presented itself (and, for the most part, unwilling to try), the abused and neglected four-year-old Tenko Shimura allowed his rage to overwhelm him, killing his sister and both parents in the process.
The orphaned child was coincidentally picked up by All For One not long afterward and was promptly groomed for greatness, while Dr. Ujiko assumedly did some tinkering behind the scenes. Shigaraki has little memory of his life before working alongside the Symbol of Evil; however, he still has access to that deep-seated anger that his traitorous family inspired in him all those years ago. Their hands are meant to serve as a reminder, allowing him to tap into the toxic emotion and fuel his potent powers even more.
The Leader of the League of Villains
Shigaraki has some serious trust issues (understandably) and is hesitant to grow his gang of delinquents, for fear of being betrayed yet again. He is not easily swayed once he sets his mind on something but is also often willing to hear the full story before making a more informed decision, such as when he questions Deku at the Mall in "The Incident." Although Stain, the Hero Killer's grand speech is enough to inspire a following from several members of the League of Villains, Shigaraki doesn't simply choose the easier option by aligning himself with the "celebrity," because he does not completely agree with Stain's ideologies. Dismissing such a lucrative accomplice for the sake of "morals and values" speaks volumes about Shigarki's character, even if he is the Big Bad.
In contrast, this villainous leader is quite quick to team up with Overhaul; although he clearly places no trust in his newest associate but recognizes that he may need to play nice this time around to gain an advantage. As unlikeable as Overhaul may be, he possesses some valuable Quirk-nullifying equipment and a particularly strategic mind which essentially inspires Shigaraki to begin making long-term plans instead of focusing on immediate gratification. Even though Overhaul goes out of his way to degrade Shigaraki in front of his own League, the young leader does not let his emotions overwhelm him and remains quite collected through their negotiations. However, all that suppressed frustration is released at full force towards the end of their partnership, as Overhaul is brutally mutilated by Shigaraki and Mr. Compress (just to make a point.)
The ambitious scoundrel treads very carefully when allying with Re-Destro's Meta Liberation Army, having acquired some experience in the whole team-up ordeal. This particular union requires a significant amount of trust, especially considering that Shigaraki plans to take an extended leave of absence shortly after taking over the reins. When forming the new Paranormal Liberation Front, Shigaraki does his best to ensure that both sides feel represented (while maintaining majority control with his League of Villain Lieutenants taking on the most authoritative responsibilities.) There may be some disgruntled subordinates within the ranks of this villainous army, but as long as Shigaraki can keep Re-Destro on his side, things should work out quite well for the fresh-faced Symbol of Fear.
The Symbol of Fear
Since being humbled by Stain, Overhaul, Gigantomachia, and Re-Destro (who all gave Shigaraki a relatively hard time by refusing to automatically accept his self-proclaimed status), All For One's prodigy has received a significant confidence boost, and the effects are visible! No longer burdened by the weight of his last, the white-haired warrior proudly shows his face to the world in “Tomura Shigaraki: Origin,” and it's all downhill for the Heroes from thereon out!
Empowered with an enhanced physique overflowing with potent Quirks, All For One's new wielder is an unstoppable force, a fact of which he is clearly aware. Although his Awakening doesn't go according to plan, Shigaraki steps into his new role quite seamlessly; apparently already possessing a thorough understanding of his new capabilities. Although he may have been submissive to his previous master, the Symbol of Fear does not roll over to All For One's will and stands his ground as the main man in this whole equation. Unwilling to be controlled by the voice within, Shigaraki boldly makes his claim as the most destructive villain in My Hero Academia history, the anxious shadow of his former self abandoned in the pursuit of better things. This power dynamic may change significantly in "The Ones Within Us," however Shigarki is unlikely to relinquish his newfound freedom without a fight.