League of Villains: Undercover

League of Villains: Undercover is a one-shot spin-off manga written and illustrated by Kohei Horikoshi that serves as a prequel to My Hero Academia: Heroes: Rising that stars Nine.

Synopsis
Nine is shown sitting alone near an abandoned alley while observing a storm tearing apart a local park. Nine monologues that the storm calms his soul and believes that the world around him will soon fall apart like dissolved mud. Sometime after that event, Nine decides to approach Doctor Ujiko of the League of Villains.

Doctor Ujiko tells the young man that despite having a Quirk that resulted in the destruction of his body's cellular tissues, he has managed to live out a normal life without anyone noticing anything peculiar about him. For these reasons, it is revealed that Nine has been selected to be a test subject for Ujiko's latest experiment that will enhance both his Quirk and body. Doctor Ujiko then questions Nine why did he accept his request, to which Nine bluntly refuses to explain his reasons at first. However, Doctor Ujiko points out that keeping secrets will only disqualify Nine from the experiment, which forces the latter to finally open up about his past.

Nine explains that his Quirk Weather Manipulation allows him to control the weather but he feels like he's stuck to the ground. In other words, Nine points out that the moment someone comes into existence, they can't decide to choose for themselves, even with so much power put into their hands, as the society around them will crush them in the end. Nine also reveals that he's seen people who were also oppressed by the superhuman society they live in, apparently suffering the same way as he once did.

Nine admits that he feels like the current society existing is a mistake, intriguing Doctor Ujiko even further. Nine then shows his belief that a true hero society should only be one where the supremacy of one's Quirk is the only way of measuring a person's worth and that both heroes and villains are irrelevant. With that being said, Nine resolves to turn everything back to whence they originally came from. Doctor Ujiko then concludes that Nine is definitely a perfect candidate, noting that his mind and body are in the right condition.

Sometime after his meeting with the League, Nine rests inside an unknown machine, undergoing the experimentation process Ujiko planned out for him. The villain inner monologues that despite not knowing what the experiment would do to him, he feels like everything will turn out fine. As Nine is sealed up for the experiment, he notes that he will create an ideal world not only for himself but for his teammates as well. While losing consciousness, Nine is unaware of All For One and Tomura Shigaraki walking past the experimentation room. Tomura takes a brief glance at Nine, who declares that he'll destroy anything standing in his path.

Chapter Notes

 * This chapter explains the reasons behind Nine's motives for wanting to destroy hero society.
 * Brief glances of each one of Nine's teammates' backstories are shown.
 * It is also revealed that Tomura once encountered Nine before the events of the main series, which was later referenced briefly in Chapter 242.

Characters In Order of Appearance

 * Nine
 * Daruma Ujiko
 * Chimera (flashback)
 * Slice (flashback)
 * Mummy (flashback)
 * Tomura Shigaraki
 * All For One