Normally when you write a story, you start at the beginning. However, in the case of the Gundam: The Origin anime adaptation you start before the beginning. That said, the results in the Chronicle of Char and Sayla prove that this approach can definitely work.
For those unaware, Gundam: The Origin was a manga retelling of the original Mobile Suit Gundam penned by Yoshikazu Yasuhiko. The manga changed and moved many events around compared to the original anime and it also more importantly fleshed out large chunks of the original backstory.
In the manga of Gundam: The Origin, it starts where the original anime series also begins and broadly follows much the same route, though with some interesting improvements.
However, a good chunk through the manga we delve into the past of Char Aznable and how he came to be the feared Red Comet. It is here where this anime adaptation of Gundam: The Origin starts and it's a fascinating angle to take on the narrative.
This is because Char’s real name is Casval Deikun and he was the son of Zeon Deikun, this being the spiritual figurehead of the space colonies and someone who fought hard for their independence from Earth rule. Unfortunately, Zeon Deikun’s financial backers were the power hungry Zabi family.
They ended up assassinating Zeon Deikun and used his death to create the Principality of Zeon and start a war with the Earth Federation, in the hopes of creating an empire of their own.
In the original Mobile Suit Gundam, none of this is shown and only referenced by things certain characters say, namely between Char and his sister Sayla. In addition, much of how the early parts of the conflict between the Principality of Zeon and the Earth Federation played out was never animated and it is here where this Gundam: The Origin adaptation is so important.
While Gundam: The Origin is effectively an alternate version of the events in the original Mobile Suit Gundam, it does cover much of the important backstory that leads up to the events that would transpire in the brutal One Year War.