The Witch From Mercury is different from the previous entries in the Gundam franchise because it decided to add some new stuff while also trying to retain some of the familiar story elements that we all know and love from the Gundam series.
The most obvious change is the fact that for the first time ever, the main character is now a girl. Not only that, the role of a masked person that was started by Char Aznable back in the original Mobile Suit Gundam and has always been an integral character in every major Gundam series ever since, is now also given to a female character as well.
Other than the characters, another notable change is the setting. The story is still set in space, but rather than taking place during a major war or times of great turmoil, the world of The Witch From Mercury is relatively at peace, at least from what we’ve seen thus far. This is why the main character, also for the first time in the series, gets to enroll and enjoy living the life of a regular student.
As for the familiar story elements, other than the aforementioned masked character, the story of this new series still tackles some serious topics, just like the other series that come before it. For example, Gundam 00 is about the civil war and military intervention, Gundam G Reco is about the monopoly on limited energy resources, and Iron-Blooded Orphan is about inequality and child labor, just to name a few.
In the case of The Witch From Mercury, it decided to tackle some of the topics that are somewhat familiar with what we’ve seen in the real world today, such as the emergence of disruptive technology, unchecked economic powers of mega-corporations, and a billionaire’s abuse of power, among other things.