Warning! Spoilers for My Hero Academia below.
In the incredible world of My Hero Academia, Izuku Midoriya didn’t initially enjoy being called Deku, as it was an insult from his childhood bully and rival Katsuki Bakugo. However, after completing his first trials at U.A. High School, Ochako Uraraka told the hero she liked his nickname and saw a different meaning behind it, leading Midoriya to reclaim Deku as his hero name.
The earliest adventures of My Hero Academia featured Deku meeting the powerful All Might and showing the famed hero he’s worthy of being his successor through an incredible act of courage. Despite being born without a Quirk, the hero-obsessed Deku risked his life to save Bakugo from the throes of a monster. In doing so, Deku captured the attention of All Might, who agreed to train him and grant him powers, leading him to get into U.A. High School and becoming the hero he always dreamed of being.
In the first arc of My Hero Academia by Kohei Horikoshi, Deku begins to make friends after completing his first trials under Eraser Head. After briefly encountering him at U.A. and in classes, Ochako introduces herself to Midoriya, where she confirms he goes by Deku. He explains that his real name is Izuku and Deku was a name given by Kacchan for being a bully, as it was an insult for not having powers. Noticing Ochako likes how Deku sounds, Midoriya is more than happy to go by the name, despite its derogatory meaning.
As the My Hero Academia anime explains, Deku is supposed to be an insult, as its Japanese translation essentially means useless or “not being able.” However, Ochako says it sounds similar to dekiru, which has the opposite meaning of “to be able.” So, while Deku told Ochacko the name was fine because he was nervous around her, he eventually adopts the title as his hero name as it’s a great way to reclaim the nickname that was originally intended to be an insult. Midoriya turned a negative into a positive and embraced his humble beginnings.
Midoriya’s hero name is just as unlikely as his path to becoming a hero. Deku was originally hurled his way by Bakugo as a way to belittle him for not having a Quirk. However, after Ochako told him she liked the name, he decided it was a fitting moniker to go by and decided to use it as his hero name. In My Hero Academia, Deku fits Midoriya like a glove, despite its somewhat unfortunate origins.