League of Villains#
All For One#
Kyudai first met All For One after he was ostracized from society due to his Quirk Singularity theory. Upon meeting him, Kyudai viewed him as a god incarnate walking among men because of his power and presence.[1] Because he was the only one who believed his theory, Kyudai devoted himself entirely to All For One's cause, giving him his original Quirk and working with him for several decades. All For One and Kyudai are shown to be genuine friends with each other. Kyudai uses his talents as a doctor to help rebuild All For One's body after his battle with All Might.
He also creates Nomu and searches for Quirks for All For One to use. All For One is the only one that Kyudai entrusts with his 'children' (Nomu) and the knowledge of his appearance.[2]
Tomura Shigaraki#
Kyudai was present when All For One rescued and adopted Tomura as an apprentice. It was he who gave Tomura the amputated hands of his family.[3] Upon witnessing the young boy violently break down at his family member's remains, Kyudai offers to fix Tomura by modifying his memory but All For One declines this offer, wanting Tomura to hold onto his emotions and rage so he can learn to direct them.
Kyudai does not hesitate to tell Tomura that he is still inexperienced, pointing out he has been spoiled by Kurogiri and that, for all the support he and All For One have given to him, Tomura still hasn't accomplished anything notable. While Kyudai admits that he doesn't hate or dislike Tomura, he still demands to know why he should provide the young villain his assistance, proving that Kyudai still sees him as inferior to All For One despite being personally chosen and raised by him.[2] However, out of loyalty to All For One, Kyudai accepts Tomura as the new leader of the League of Villains and admits he is willing to provide his services to him. He is especially impressed by the willingness and desire of Tomura to destroy society, although still demands that Tomura prove himself by taming Gigantomachia.[3]
After Tomura accomplishes his goal, he contacts Kyudai and the doctor notes on how Tomura exceeded his expectations with regaining his memory, his recent victory over his opponents and the benefits it acquired, as well as making Gigantomachia see Tomura as a true leader. From here, Kyudai agrees to give Tomura his full support and grant him further power.[4]
Kyudai's devotion to aiding Tomura becomes so strong that he outright admits that he has only continued living for his sake.[5]
Gigantomachia#
Kyudai was left in charge of controlling and monitoring Gigantomachia after All For One decided to hide him after foreseeing his inevitable downfall.
Kyudai knows that Gigantomachia is extremely violent and loyal to a fault to All For One, and therefore controls him with recordings of his master's voice on the radio that Gigantomachia carries on his neck. Kyudai at times refers to Gigantomachia as "Machia".[2] Kyudai believes Gigantomachia is useful to Tomura's goals and refuses to lend his full support until Tomura gets Gigantomachia to submit.[2]
Johnny#
Kyudai was saddened by Johnny's death and called him a friend. He described Johnny as being curious and complimented him, showing that Kyudai had a sense of kinship with his creations.[6]
Dabi#
Kyudai meets Dabi when he warps him to his laboratory along with the rest of the League of Villains.[2] Kyudai is impressed by Dabi's keen eyes and ability to discern the difference with the High-End Nomu, and actually goes so far as to enlist his help to test out a High-End Nomu. Dabi is the only member of the League of Villains besides Tomura that Kyudai shows any interest in.[3] Kyudai later uses Johnny to warp Dabi away following the fight against Hood[7].
It is revealed that Kyudai had known Dabi before he became the villain he is now. When Toya nearly burned himself to death, he was rescued by All For One and Kyudai restored his body the best he could, although severe damage still remained. Toya was brought to a nursery to raise children as “spare vessels” for All For One in case anything happened to Tomura. Toya however refused to learn anything from them and set fire to the daycare before running away. Kyudai remarks that Toya’s desire to impress his father couldn’t be manipulated even by All For One, and says that they didn’t expect him to last for a month with his burned and damaged body. To Kyudai’s surprise however, Toya lived on and became the villain known as Dabi. After reuniting with him and introducing Dabi to his High-End Nomu, Hood, Kyudai realized that Toya’s desire for revenge against his father was the only thing that kept him alive.[8]