How did hero-in-training Oboro Shirakumo die in Bones Inc-produced anime TV adaptation are set in a world in which around 80% of the human population possess superpowers known as Quirks. Consequently, much of society is divided into two categories: heroes and villains, with the former group using their Quirks for the common good while the latter use their superpowers for more nefarious ends.
My Hero Academia's young wannabe superheroes must undergo training at institutions known as hero schools where they learn to hone and master their unique Quirks through a mix of lessons and work-studies. One of the most prestigious institutions in My Hero Academia is an elite training academy called U.A. High School which was formerly attended by Oboro Shirakumo – a jokey but altruistic student whose Quirk was the ability to generate clouds that could be used as a protective shield, to move about at great speed or to block an enemy’s vision.
Most of his story in Horikoshi’s main manga series is told in flashbacks, but more is revealed about Oboro Shirakumo in My Hero Academia: Vigilantes – a spinoff series written by Hideyuki Furuhashi and illustrated by Betten Court. During the spinoff’s "School Days Arc", Shirakumo was a second-year student at U.A. High School who had dreams of one day forming a hero agency with his friends, including My Hero Academia's Shota Aizawa and Hizashi Yamada. Sadly, Shirakumo died before he could see those plans come to fruition.
In chapter 63 (“Find That Resolve”) of My Hero Academia: Vigilantes, Shirakumo was on a work-study mission with Aizawa patrolling the streets of their city when a villain named Garvey launched an attack. Garvey’s attack caused serious damage to a nursery school and although Shirakumo was able to protect its children with his Cloud Quirk, he was tragically struck and killed by falling debris in the process and his body was discovered post-battle under a pile of rubble. However, Shirakumo’s My Hero Academia story didn’t end with his death.
The main My Hero Academia manga series reveals that Shirakumo’s corpse was recovered by head villain All For One and reanimated into a Nomu – a mindless, villainous super-soldier made from the heavily modified bodies of deceased individuals. The Nomu form of Shirakumo is known as Kurogiri and serves as All For One’s protector but as Aizawa discovered in My Hero Academia chapter 255 (“Hero Hopeful”), a small part of his friend remained locked inside the Nomu. However, whether Shirakumo will ever be released from his Nomu form in My Hero Academia remains to be seen.