Nariaki Utsumi is a major antagonist turned supporting character in Kamen Rider Build. He works as an engineer in Namba Heavy Industries Ltd. and a right-hand of late Juzaburo Namba. He used to be working with Gentoku Himuro and later betrayed him to become Evolt's servant and transformed into Kamen Rider Mad Rogue to have enough strength so he can avenge his mentor and save the company. As a result, he teams up with Gentoku in order to defeat Evolt. He is also ironically revealed to be a cyborg after he was shot by Gentoku.