Ryusei School

The Ryusei School (流星塾) is a group of orphans fostered by the former Chief of Smart Brain, Hanagata, and were schooled under their teacher Mr. Masuda (増田教諭), portrayed by Michihiro Yamanishi (山西 道広). These students became known as the Ryuseiji (流星児). Shortly before the series started they attended a reunion, with all students killed and resurrected as Smart Brain's "hope", with only Kusaka having memories of the night intact. They each were sent the three Rider Gears:Mari obtaining Faiz and the bulk under Mr. Masuda obtaining Kaixa. The members other than Mari and Kusaka include:

Shuji Mihara
Shuji Mihara (三原 修二) is a relatively cowardly member of Ryusei School who would rather forget about Orphnochs and go back to living a normal life. He would become the default wearer of the Delta Gear and fight as Kamen Rider Delta (仮面ライダーデルタ) despite his cowardice. After Rina was hit by a truck retrieving the Delta case he had thrown into the street, he resolved to stop running and fight alongside the others.

Shuji Mihara is portrayed by Atsushi Harada (原田 篤). Harada previously portrayed Sho Tatsumi in Kyuukyuu Sentai GoGoFive.

Others

 * Saya Kimura (木村 沙耶): A "nekojita" much like Takumi, Saya briefly wore the Delta Gear. Eventually she found her way to the Kikuchi Dry Cleaning shop and worked part-time there. She waited to see what kind of person Takumi was before deciding to hand over the Delta Gear to him. Unfortunately, she was killed by Sawada before she could. Saya Kimura is portrayed by Mai Saito (斉藤 麻衣).
 * Rina Abe (阿部 里奈): Shuji Mihara's friend, former classmate and co-worker in the orphanage where Teruo Suzuki (Orphnoch King) stayed. After the series, she, Mihara, and Mari were the only surviving Ryuseiji. Rina Abe is portrayed by Rie Kasai (河西 りえ).
 * Kyosuke Tokumoto (徳本 恭輔): After Shindo's death, he tried to put on the Kaixa belt, but couldn't out of fear because of the other users' deaths. After the Delta belt was discovered and he used it, he believed the belt was rightfully his because of the belt's side effect. Not only that, he also gained some power from the belt. Along with Arai, he kidnapped Mari to lure out Sawada to get the belt. Killed by Sawada. Kyosuke Tokumoto is portrayed by Shun Saeki (佐伯 俊).
 * Shoji Inukai (犬飼 彰司): Shoji Inukai is portrayed by Takuma Watanabe (渡辺 琢磨).
 * Kiyotaka Nishida (西田 清高): Temporarily used the Kaixa belt in episode 11 and 12. With the Kaixa Gear, he destroyed Crocodile Orphnoch's first life. But he soon died in Mr. Masuda's arms from the belt's side effect. Kiyotaka Nishida is portrayed by Yoshiaki Kawasaki (河崎 芳明).
 * Takahisa Shindo (神道 貴久): Used the Kaixa belt in episode 12 to fight the Crocodile Orphnoch, despite others' protest, but the Orphnoch knock the belt off him, forcing him to revert and disinterage from the belt's side effect. Takahisa Shindo is portrayed by Shintaro Chikada (近田 慎太郎).
 * Haruko Kamijo (上条 晴子): Haruko Kamijo is portrayed by Hiroko Hayashi (林 裕子).
 * Asami Ito (伊藤 麻美): She was killed by Kawachi when he tried to take the Delta belt. Asami Ito is portrayed by Kaoru Kurasawa (倉澤 薫).
 * Ken Arai (新井 賢): Temporarily knocked out by Kawachi. He gained power and became obsessed with the Delta belt like many other users after using it. Along with Kyosuke, he kidnapped Mari to lure out Sawada to get the belt. Killed by Sawada. Ken Arai is portrayed by Hirohito Honda (本田 博仁).
 * Yuki Kawachi (河内 勇樹): He suddenly attacked Arai and killed Asami because of the obsession with the Delta belt. But it was proven wrong since he called Kusaka to rescue him from the Frog Orphnoch. Still, it was too late. Before dying, he said that Sawada had the belt, but it was false. Yuki Kawachi is portrayed by Kenta Hinokio (檜尾 健太).
 * Shingo Ota (太田 信吾): After Mari's second death by Sawada, he constantly tried to persuade Mihara to fight with the members. Later killed by Sawada. Shingo Ota is portrayed by Takuji Kawakubo (川久保 拓司)
 * Aonuma (青沼): Transformed into the Sloth Orphnoch after the attack. Aonuma is portrayed by Kazuma Kurihara (栗原 一馬).