Tomura has a sinister and warped personality: He doesn't care for his or almost anyone else's life, having no qualms about evil deeds like killing U.A. High School students in order to provoke All Might[1] or threatening Izuku Midoriya with the death of civilians unless he cooperated with him.[2] Tomura was initially perceived to be a "man-child" by the heroes, as All Might described him as a child who likes to brag and acts out when things don't go his way.[3] He is very arrogant, selfish, dependent and demanding, becoming angry if things don't in go his way, in a way akin to a child's tantrum. Like a child, he doesn't seem to be able to cope with his own feelings, instead lashing out and abusing both others or himself, tearing at his own neck when he becomes frustrated.

Tomura likes to brag about the Nomu and the League of Villains, wanting to prove they have the power needed to accomplish their goals and taking pleasure in mocking his enemies. He retaliated Stain's attack by releasing Nomu to wreak havoc and was verbally upset when his plan failed, starting to bear a grudge against Stain and Izuku.[4] Upon meeting Dabi and Himiko Toga, he attacked them for simply mentioning Stain.[5] He later stole the Quirk-Destroying Drug and took great pleasure in mocking Kai Chisaki by pointing out he was now the very thing he wanted on others.[6]

The only person Tomura has shown compassion - apart of his closest allies latter - is his mentor All For One, having a great deal of respect and attachment to All For One. He showed great remorse in leaving All For One behind to face All Might alone.[7] Tomura has a vengeful side for his comrades, decaying and cutting the arm off Overhaul after he killed Magne. He considers most of his allies as valuable for his plans, to the point that the Eight Precepts of Deathdescribed that the members of the League of Villains care for each other.

Tomura will do whatever it takes to accomplish his goals, abandoning his disdain for Stain and adopt his ideology to enlist more members to his cause, including Dabi and Himiko. He rallies them behind the idea that they need to crush hero society as a whole after Stain exposed its false sense of heroism. He has considerable leadership skills, taking charge of the Villains by sending the Vanguard Action Squad to attack the U.A. Training Camp and eventually dealt a crippling blow to Hero Society. Eventually, Tomura became calmer and gained some self-control, being able to deal with adverse situations without throwing childish tantrums or scratching his neck. When Katsuki Bakugo exploded the hand from his face, his colleagues were afraid he would lash out. Instead, he merely put the hand back over his face.[8] 

After confronting Izuku in the mall, Tomura develops real convictions: He always had a desire to kill All Might, but it was out of an impulsive expression of anarchy towards a society which hurt him and caused his mental instability. He now realizes that All Might is what he hates about both Izuku and Stain. Tomura truly wishes for a society without All Might, feeling that the world full of Quirks is a dangerous place and that the current society may easily crumble when their Symbol of Peace dies, believing it would show how vulnerable their sense of peace is.[9]