Mobile Suit Gundam: Engineered Futures.

Engineered Futures is a Fanfic set in the Witch From Mercury timeline with the sole exception of one new character: You! Well... the protagonist of the story: Zachariah Hadiquo of Hadiquo Industries, a company who's main import is rations and foodstuffs throughout the System. This culminates into Zachariah being a low-level Spacian within Asticassia School of Technology, but he has one trick up his sleeve. With skimmed funds from his parent's coffers and years of studying Mobile Suits as a whole, Zachariah enters the school year with a workhorse of a Mobile Suit lacking any of the technological advantages that most have, made up with sheer mechanical might. Today, for the first time in Asticassia's history, a Green Giant roams the Grounds.

As the synopsis states, this entire Fanfic is just if a Zaku was in Witch From Mercury. Besides that plus being a year before the actual anime and focusing a lot more on the school stuff and added lore, nothing should be really any different. Watch the school life go, read the Mobile Suits fight, and bear witness to the scrappy underdog that is Zachariah and his ever-growing Mobile Suit.