Deku would never want to hurt his My Hero Academia allies, but a detail from the very first chapter shows that if he wanted, he could destroy them.

While My Hero Academia's central hero Deku is introduced as adoring his world's heroes, that very obsession gives him the potential to become their greatest threat, capable of taking down even Pro Heroes like All Might.

In My Hero Academia #1, it's revealed that in addition to taking notes in class, Deku has also been taking notes to memorialize his observations and analysis of his classmates, his teachers, as well as other Pro Heroes he has come across. These notes are compiled in what Deku has entitled his Hero Analysis for the Future. As of Chapter #1, Deku has already completed 13 volumes of observation and analysis, and there is no indication over the course of the manga that he has ever stopped his journaling tendencies. That means Deku is likely to have complied the single most comprehensive understanding of current and future Pro Heroes' abilities and weaknesses ever. Indeed, the journals should surpass Hawks Villain Report as a source of unrivaled My Hero Academia intelligence.

With the unadulterated, "fly on the wall" knowledge that Deku has been able to assemble in his journals, it's likely that a careful review of the information would reveal the weaknesses and vulnerabilities of every member of Class 1-A, as well as the teachers and Pro Heroes that normally interact with the class such as All Might, Eraserhead, and the Wild Wild Pussycats. Although Deku was more than likely taking these notes to better himself as a fighter, as well as facilitate the improvement of his classmates, they naturally could be used by an evil, crazy, or co-opted Deku, to figure out ways to defeat his classmates and colleagues with minimum effort. Deku's observations are even shown to contrast different heroes' powers against each other, moving past mere information gathering and into tactical thinking. It's the type of intelligence All For One would love to have access to.

Assuming Deku is as observant and relentless as he shows himself to be in fighting, helping others, and wanting to be the best, there is no ceiling to what his journals could contain. For instance, based on the events of My Hero Academia #337, Deku is likely one of the only people who has seen Invisible Girl's face, meaning she couldn't escape him by hiding in plain sight. Similarly, Deku most certainly has kept copious notes on his childhood rival Katsuki Bakugo, who has confessed psychological weaknesses few others know.

Naturally, Deku so far has not exhibited the personality that would make fans suspect that he would turn on his classmates, but All For One has shown a great deal of interest in influencing him. With unparalleled inside knowledge of the current and next generation of heroes, Deku's notes make him a ticking time bomb which - if ever turned against his My Hero Academia allies - would make him their greatest threat.

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