Deku planned to become a hero long before he even received a Quirk. Before the events of My Hero Academia even began, he'd spent years studying the Quirks of Pro Heroes and brainstorming how best he could apply their principles in combat. He compiled everything he learned in several notebooks and the worth of his research has already been proven several times over. Deku's studious note-taking has inspired several new moves for not only himself but many other characters as well.
Deku's attempts at studying his way into becoming a hero might have seemed pathetic at first but it was the very trait that allowed him to catch All Might's eye. Against the overwhelming power of the sludge villain, it was his iteration of Kamui Woods' Pre-Emptive Binding that allowed him to stun his foe and get close enough to give Bakugo some breathing space. His bravery in the face of danger inspired All Might to push past his limits and defeat the sludge villain for good.
At UA, Deku's Quirk analysis continued to be a force to be reckoned with. He came up with the idea for Fumikage Tokoyami to use the primarily offensive Dark Shadow as a shield during the Cavalry Match at the UA Sports Festival. Deku's strategy was largely successful and that spurred Tokoyami to develop it even further. He began experimenting with using Dark Shadow to bolster his low physical strength. After a few months of practice, he perfected his new signature move: Dark Fallen Angel. By coating himself with Dark Shadow, Tokoyami greatly increased his strength and speed. He credits Deku as being the one to first suggest using Dark Shadow defensively.
Deku's years of practice analyzing Quirks and out-of-the-box thinking also inspired some really cool combo moves for his classmates. During the League of Villains' attack on their summer training camp, Deku and his classmates needed to capture the swiftly fleeing Mr. Compress. On the spot, he came up with the idea of using Ochaco Uraraka's Quirk to reduce their weight so Tsuyu Asui could fling them farther. He planned for Uraraka to release her Quirk when they were close enough to their target so their sudden weight would increase their acceleration.
Deku's plan worked like a charm. It was so successful that Uraraka and Tsuyu continued to use it during their internships and work studies, albeit with a few modifications. They combined Uraraka's Meteor Shower with Tsuyu's astonishingly strong tongue for devastating aerial attacks that villains never saw coming; A move they called Meteor Fafrotskies. They also use a variation of this same strategy to deal with more complicated villains, dropping them from heights in controlled falls designed to stun them into unconsciousness.
His notebooks are also incredibly useful outside of the battlefield. His format of note organization was adopted by All Might himself when he was organizing notes on the previous One For All Users for Deku to study. Jiro also asked for his input when she was making notes for their classmates’ band performances. With Deku's help, her notes enabled her classmates who were mostly newbies to music put on a spectacular show for their school festival.
