WARNING: The following contains spoilers for My Hero Academia Chapter 286, "The Ones Within Us” by Kohei Horikoshi, Caleb Cook and John Hunt, available now in English from Viz Media.
My Hero Academia's Midoriya Izuku is generally one of Shonen’s more laid-back protagonists. He's as focused on his main goal of becoming the greatest hero as any other MC, but otherwise he has a very easygoing character. Quite warm toward friends and strangers alike, Midoriya also has a bit of a temper about him. The easiest way to trigger his anger is to threaten the well-being of those closest to him.
If there's one point My Hero Academia has sought to drive home, it's the importance of the bonds of friendship. Most of Class 1-A may not have known each other before entering UA, but they became fast friends. They've crossed many hurdles together and Midoriya has shown a fondness for each of them, as they're probably his first friends with whom he's on equal standing.
Deku's Growth Often Stems From Aiding His Classmates
A lot of Midoriya's biggest steps forward in mastering One For All happened as a result of his urgency to save a classmate in danger. The first time he managed to properly control OFA was a punch aimed at Shigaraki Tomura. During the USJ attack, the villain attempted to use his Decay Quirk on Asui Tsuyu, prompting an aggressive response from her friend and classmate. Midoriya's punch was intercepted by Shigaraki's Nomu guard, but judging by the shockwave it produced, it certainly would have put Shigaraki out of commission for some time. It was a lot more power than Midoriya had previously been able to summon and even more impressively, he did so without breaking a single bone.
Similarly, during Midoriya's encounter with the Hero Killer, he had to fight knowing his victory or defeat might spell the same fate for both Iida Tenya and Todoroki Shoto. Despite facing an opponent far more experienced in combat with his then-unrefined Full Cowling, Midoriya never faltered. He broke free of the Hero Killer's paralysis twice and adjusted his maneuvers mid-battle to counter Stain's wraith-like technique. Midoriya's battle with Stain was the first real test of his Full Cowling move and it performed admirably.
MHA Chapter 286 Delivers Deku's Rage Moment
Almost every anime has a famous rage moment. The most memorable are often triggered when the character loses the battle of control for their body to a malevolent force they barely understand anything about. My Hero Academia's rage moment comes when the protagonist is in full control of his actions, but is perhaps a lot more bloodthirsty because of a loss he's suffered. In Midoriya's case, it's the presumed death of Bakugo Katsuki, who was impaled by an attack from Shigaraki that he'd rushed to receive in Midoriya's stead.
Midoriya's mood switch was instantaneous. In a matter of seconds, he completely turned the tide against Shigaraki who'd previously been handling several Pro Heroes alone. However, being blinded by rage didn't mean Midoriya was fighting any less intelligently. To prevent the dangerous amount of One For All he was currently using from completely wrecking his body, Midoriya wrapped tendrils of Blackwhip around his arms and legs. This strategy allowed him to land several blows on Shigaraki, maximizing the force he could use while reducing the threat to his fragile arms.
The sudden power boost he received was One For All responding to Midoriya's anger over Bakugo's injury. When Midoriya first used Blackwhip, he learned from its original holder, Daigoro Banjo, that his power would swell in strength depending on the emotional state he was in while using it. He'd experienced this previously on multiple occasions but having Banjo finally explain how it worked proved these weren't just flukes. Midoriya's big fight with Shigaraki remains his greatest feat of strength in My Hero Academia to date, and the power he was able to produce speaks volumes about how much he treasures not only Bakugo, but his friends as a whole.