Prelude - Tournament Kamen Rider.
Nero Samson - Kamen Rider Den-O.
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Nero Christopher Samson was a 19-year-old son of a semi-retired police detective and a former waitress. Nero was born in Plymouth, Michigan, but was raised in Saagen Town, a quiet place in Detroit that usually didn't see crime. Not all of Nero's life was good; he lost his best friend Charlie in a house fire during a sleepover when they were both aged five.
Nero grew up around the detectives his father worked with and it was quite a cast of characters. He couldn't help but imitate them.
"Ore Sanjou!"
"Boku ni Tsuraratemiru?"
"Nakerude!"
"Kotae Wa Kiitenai!"
At age seven, Nero lost contact with the funny detectives, but little did he know that his father Drake kept contact with them, working incognito on several cases.
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Nero's uncle was Thomas, Drake's brother, nicknamed 'Tomcat' after the cartoon Tom & Jerry. Thomas was a baker, working from restaurant to restaurant, sandwich shop to sandwich shop. It continued like this until Tomcat got fed up and just opened his own place in Saagen Town, which became very popular... with the townspeople and Nero, who couldn't get enough of Tomcat's cooking.
And a friend of the family, Professor Jack Jeffrey Ryker, was as much a part in Nero's growing up as his parents were. Ryker was so inspiring for Nero, having sold a best-selling book commercially and settled down in Saagen Town with the money he had made. Nero refers to Jack as 'Sempai', something he remembered from the detectives. To add to that, Jack was previously a teacher at Nero's high school.
For reasons unexplained to Nero, his father signed him up to a dojo in the town at age 13. A tough regiment and constant exercise kept Nero going for six years. About four years in, Nero found out that his father was planning to compete in the upcoming Tournament Kamen Rider competition, but a bone-breaking injury put an end to those plans because Drake had his legs broken. Knowing he had dojo experience under his belt, Nero decided to go in his father's place, along with his two best friends, Chad 'Phoenix' Leiter and Taryse Evans, who he had known since high school.
Nero wouldn't mind getting competitive with his friends, but they went along with it because they had set pretty high standards for themselves as well. Nero hated to lose, but he also hated to see his friends' morale get really low.
Nero knew Tournament Kamen Rider was the brainchild of Professor Jack and that Jack was good friends with Drake. Not only that, but monstrous creatures were popping up everywhere; ones who can appear from sand, ones with stained glass appearances, green ones, etc. Jack explained that the Tournament was a good way to dwindle these numbers.
Drake showed Nero the belt he would've used in the tournament after he broke his legs: the silver-coloured Den-O Belt. Drake informed his son that he had to send it back to Jack.
To Nero's surprise, Jack selected Nero to use the Den-O Belt in his fathers' place. And after Jack had explained the rules at the official gathering, Tournament Kamen Rider began for Nero and his friends.