Johnny Yoo

Johnny Yoo is an international celebrity and stunt coordinator who uses his Ninjutsu abilities to gain fame and status abroad, eventually becoming a benefactor and partner to the Konjo Group. He's also one of the holders of the Seven Shinobi Hyoutans, using it to transform into Kamen Rider Bakugo.

Childhood
Many years ago, a young Johnny was running away on the streets, only to be cornered by a Nin-Ju who proceeds to devour his mother. He, however, would be saved by a Silver Rider, but not before learning that the Nin-Ju was in fact his father. He would also misinterpret the act of sealing a Nin-Ju as the Rider hiding the truth from people, as his testimonies about her mother's death would fall on deaf ears due to the unbelievable circumstances it detailed regarding monsters.

Sometime in his teens, he would actually learn about Ninjutsu, being one of the many who was affected by the Blood Storm in 2011. Unlike the other people who would use ninja abilities practically, he'd instead move to different countries and use Ninjutsu to gain fame and recognition, first as a stuntman, before rsing to become an international celebrity. He would also come across the Clay Hyoutan through unknown means, allowing him to become a Kamen Rider himself.

Events in Hero Retold
Johnny would eventually return to Japan, having raised his stock to become one of the partners and benefactors from the Konjo Group. He would first visit the events area to view the group's preparations, eventually meeting Iroha at the stage and later, the Vice-CEO of the company as well.

Days later, Johnny would come to the said event until a Nin-Ju attacks the premises. With flashes of his childhood coming back, he'd angrily punch the Nin-Ju and transform to Kamen Rider Bakugo to get revenge for her mother. He'd also encounter Shinobi, and while he was initially confused due to his color being different, when the Rider used the Sanzu Sealing Technique to seal the Nin-Ju, he'd become convinced that it's the same Rider, before charging to attack him.

More info to be added

Personality
Initially, Johnny appears to be cool and collected, often interacting with people politely and is well-meaning towards people he meets. He's also quite the showoff, often using his Ninjutsu just to get attention and be cool in front of many people; a trait which irks Isamichi a bit since Johnny reminds him of his former self. Deep inside, however, he's often haunted by his horrific childhood and would have nightmares about the past events. Though he has seemingly buried his grief through his fame, upon seeing the Nin-Ju and Shinobi once again, he acts aggressively, often not listening to reason, and instead focuses on his revenge.