Nariaki Utsumi

Nariaki Utsumi is the assistant of Gentoku Himuro at the Touto Institute of Advanced Matter Physics and a member of the organization Faust. He later defects over to Namba Heavy Industries Ltd. after being used as a scapegoat by Himuro.

Reporting to Gentoku
Utsumi is first seen informing Gentoku about Sento's job application for the Touto Institute of Advanced Matter Physics, stating that Sento had passed the entrance test with a perfect score.

Utsumi is Sento's direct superior at the Institute, reporting directly to the Prime Minister of Touto, Taizan Himuro, while at the same time also secretly assisting Gentoku/Night Rogue within Faust. He was one of the first present witnessing Taizan's collapse, after the Pandora Box was stolen from the Institute. The Box was later hidden within a secret basement at one of Namba Heavy Industries' laboratories.

The Fall of Faust
After the Pandora Box was stolen by Blood Stalk, Night Rogue and Juzaburo Namba resolved to dissolve Faust by staging an operation to destroy it where Touto would supposedly take down Faust. In the operation Utsumi assumed the identity of Night Rogue and was exposed by Build as Faust's apparent leader, but Build remained suspicious.

Cornered by Build a bridge across a river, Nariaki revealed to Build that he had known for a while he was really Sento. He told Sento to "turn back" while he still had time but was shot by Himuro and knocked off the bridge before he could finish.

Working for Namba
However, Nariaki was later found by Blood Stalk and recruited into Namba Heavy Industries Ltd. He later revealed to Himuro that he had survived while he was waiting for Juzaburo Namba.

After Himuro was banished from Touto, he approached Utsumi and asked to be made a Kamen Rider, Utsumi accepted his request, but made him plead for it as revenge.

Collaborating with Seito
Utsumi later updated the Kaiser System to create the Remocon and Engine Bro's to be used by Seito's military. For his efforts, Utsumi received a personal thanks from Seito's Prime Minister, Masakuni Mido.