My Hero Academia's Izuku (Deku) spent a lot of time studying how other people's Quirks worked before getting one of his own, and it paid off big time.
Prior to receiving a Quirk, Izuku had aspirations of becoming a hero. Prior to the occurrences of MHA, he'd spent years learning about the Pro Hero Quirks and figuring out how to best employ them in battle. He kept meticulous notes on everything he discovered, and the value of his work has already been demonstrated time and time again. Deku's meticulous note-taking has resulted in a slew of new moves for numerous characters, including himself.
While Deku's attempts to learn how to be a hero first appeared pitiful, it was just this trait that allowed him to be noticed by All Might. Bakugo's Pre-Emptive Binding stunned the sludge villain long enough for Kamui to use his variation of Kamui Woods' Pre-Emptive Binding against him. All Might was inspired by his fortitude in the face of danger to go beyond his limitations and end the slime villain's reign of terror once and for all.
With Deku's Quirk study, the UA became an even more formidable opponent. During the Cavalry Match at the UA Sports Festival, he had the brilliant idea of having Fumikage Tokoyami employ the attacking Dark Shadow as a shield. Tokoyami was inspired by Deku's strategy because it was generally successful. As a means of improving his shaky physical strength, he turned to Dark Shadow. The Dark Fallen Angel became his new signature move after months of preparation. Tokoyami's strength and speed skyrocketed after donning the Dark Shadow armor. He gives thanks to Deku for the idea of deploying Dark Shadow as a defensive technique.
Years of Deku's practice examining Quirks and thinking outside the box have also inspired his students to come up with some very unique combo moves. Mr. Compress was on the run when the League of Villains attacked their summer camp, and Deku and his classmates were tasked with catching him before he could get away. To make Tsuyu Asui throw them further, he devised a plan to use Ochaco Uraraka's Quirk to lighten their load. When they got close enough to their goal, he had Uraraka use her Quirk, which increased their speed because of the unexpected weight.
Deku's strategy was spot on. As a result of its effectiveness, Uraraka and Tsuyu have continued to use it during their internships and work studies, albeit with a few changes. Together with Tsuyu's extraordinarily strong tongue, they created a devastating aerial attack that the bad guys never saw coming: Meteor Fafrotskies. A variation of this approach is used to take down more difficult criminals by lowering them from a great distance to make them stunned and unconscious.
Outside of battle, his journals are immensely valuable. The approach he used to organize his notes on the previous One For All Users was used by All Might when he did the same thing for Deku. Also, Jiro solicited his opinion when she was jotting down notes for the band performances of their peers. They put on a great presentation for their school festival thanks to Deku's suggestions and the support of their newcomer classmates.
Littleowh hopes that the material provided above is entertaining and valuable to readers.