Ai Asuka
Shin's girlfriend and nurse at the ISS (Institute of Super Science) where the experiments are held. She tells Shin of the conspiracy, only later to be killed while pregnant with Shin's child. With her dying breath, she tells him to protect the child at all costs, for it is now a target of the syndicate due to its mutation (it shares a telepathic bond with its father).
Takuya Yuuki
Shin's friend, who urges him to escape from the experiment while he still can.
Dr Daimon Kazamatsuri
Shin's father. Geneticist, not completely aware of the grave situation he put his son in.
Sarah Fukamachi
A CIA agent who tracks Shin and those connected to ISS/the syndicate.
Series:  Shin Kamen Rider: Prologue