Bundorio Bunderas, often called Bunbun, is an alien machine lifeform, mechanic, and former Big Bang Grand Prix racer. He works with Taiya Hando to develop the Boonboomgers' systems and serves as the heart of their garage.

Bundorio supports the team as a strategist, builder, and combat partner. His past with Hashiriyan and Waruido Spindo becomes central to the final stage of the conflict, making his bond with Taiya one of the team's most important connections.

Byun Diesel is Sakito Homura's alien partner and a fast moving machine lifeform tied to interstellar racing and transport. He works alongside Sakito after the two arrive on Earth.

Byun Diesel supports Bun Violet in combat and serves as the core of ByunByun Mach Robo, giving the team an additional mecha partner when the Hashiriyan threat grows stronger.

Shirabe Saibu is a special investigator connected to the International Space Agency. She monitors the Boonboomgers' activities and often acts as the official point of contact between the team and larger space authorities.

Although she begins as an observer and investigator, Shirabe's relationship with the Boonboomgers develops as she sees their commitment to protecting Earth and completing their missions.

Aki Nogi is one of the people connected to Delivery-Ya's wider circle of clients and allies. Like many of the team's customers, Aki becomes part of the Boonboomgers' world through the team's mission based delivery work.

Maimi Baisu is an ally connected to international space affairs during the Boonboomgers' fight against Hashiriyan. Her role reflects the expanding scale of the conflict as the team's battles move beyond ordinary Earthbound incidents.

Nicola Keydoor is an ally from beyond Earth who becomes connected to the Boonboomgers during the later stages of their mission. Her involvement helps reveal the broader interstellar stakes surrounding Bundorio, Spindo, and Hashiriyan.