Mako Reactor is one of two things:
In the game Final Fantasy VII:
It is a power plant which takes its energy directly from the planet; the planet's "life energy" is called Mako, and it pools in certain areas around the Planet. Unfortunately, the Earth only has so much Mako, and if it is deprived of it all, life will cease to exist, and the Planet will die.
It is also the name of a pop-punk band from Valparaiso, Indiana. http://www.makoreactor.8m.com