Doctor Hoshi, an astronomer at a Japanese observatory, initially faces skepticism from colleagues for his belief in extraterrestrial life. This conviction proves true when he discovers the crashed ship of Maya, an alien woman from the destroyed planet Katharos. Her world fell to the resource-plundering Blasters, who now target Earth. Hoshi aids Maya, sparking an interspecies romance that leads to marriage and a hybrid son, Kantaro Hoshi.

Maya dies from radiation exposure during the creation of Ganger, a sentient living-metal robot built to defend Earth. Hoshi raises Kantaro alone, prioritizing moral values like compassion over vengeance despite Blaster-inflicted trauma. He invents a distinctive pink motorbike for Kantaro, enabling transportation and connection with Ganger during battles.

As the Blasters invade, Hoshi serves as a scientific advisor, relaying tactical and astrophysical guidance via walkie-talkie during Ganger's fights. He oversees Kantaro’s operational integration with Ganger to maximize combat effectiveness. His prior research into Blaster technology and motives proves critical in identifying their weaknesses.

Motivated by Maya’s sacrifice and Earth’s protection, Hoshi embodies calm, reasoned authority. He consistently advocates non-violent resolutions and counsels Kantaro against rage, reinforcing the value of all life. His character arc centers on upholding Maya’s legacy through scientific ingenuity and ethical leadership during planetary conflict.