Reactor Mights are mysterious particles found in space that was said that six were formed during the birth of the universe, three Light, three Dark. They possess power that exceeds any lifeform possessing them, and they can also be housed inside F-Zero machines, causing them to have extensive speed and power. They're so rare, that they cannot be easily found with advanced technology.
Role in the anime
Black Shadow and Captain Falcon were the only racers that know of the Reactor Mights' prowess prior to the events of the anime. The Emperor of Brutality was first shown to use one possessing darkness upon Zoda's awakening from cold sleep 150 years ago. Although he woke up five years before Rick, he was then transformed upon contact of a Reactor Might.
From there, Capt. Falcon went to Dr. Stewart and Jody Summer personally and revealed of how the Reactor Mights came from and how they're being harnessed. He said in the 23rd century, chaos would be unleashed the universe over, and he counted on them to house a Reactor Might of light inside the experimental Dragon Bird invented by Dr. Clash. Eventually, Rick was awakened, and since he has a connection with Zoda, he was chosen to handle its hidden potential.
During Rick's training with Falcon, it was discovered the Blue Falcon also had a light Reactor Might. It was also when he discovered of the secret technique known as the Booster Fire, a rapidly-spinning ability that enables an F-Zero machine to have immense power and speed; however, because of the extra input it produces it can only be used once per race, otherwise the vehicle would lose control and balance.
Three Dark Reactor Mights were found in three sources, a secret lair eventually located by Blood Falcon and Capt. Falcon before the latter's disappearance, Zoda turning him into Hyper Zoda, and the Black Bull. It was also known that they can cause a victim to hallucinate, and sometimes retain lost memories; like when Miss Killer recalled herself as Haruka Misaki, or Rick suffering from exposure by Hyper Zoda. They, too, can erase a victims' memories utilizing a stasis tube and submission, hence it was how Haruka became brainwashed after cold sleep, reducing her to being born to Black Shadow. Rick had a close call before he ignited and escaped from it after his friends gave him indirect support. Haruka then found out about Black Shadow's dream using the code, REACTORMIGHT, on an encrypted hatch.
Rick was destined as the savior of the galaxy, collecting all six Reactor Mights. His Dragon Bird was upgraded to the Dragon Bird EX that could house two Mights, much as the Black Bull during a lethal race. A Reactor, as well as the Core, were created to hone the power of all Mights, as a way for Black Shadow to incinerate and enslave the universe within an instant. Though his dream was thwarted after Rick utilized a Reactor Might to its full power, as well as Falcon's sacrifice.
Rick's and Falcon's use of a Reactor Might is known as the Booster Fire.
Zoda becomes Hyper Zoda, and his machine transforms from the Death Anchor to the Hyper Death Anchor, and his attack is the Death Fire.
Black Shadow's version is the Black Fire.
Role in F-Zero Climax
After the first lap of a race is complete, the player can use a Reactor Might to perform a Booster Fire. The machine can save them during a race, or use one at a time within each lap finished before the race is done. It can be used when the player taps the booster button twice, causing it to perform a rapid spin attack and a great increase in speed for a brief period of time. It's likely a machine may get destroyed within the vicinity of one. Each machine surrounds itself with a different hue; for example, the Dragon Bird is white, the Black Bull is a dark violet, Blood Hawk is red, etc.