I’m going to start the Core Gundam Cleanup by building the Mars Armor, since it’s the one of the two that’s already complete and ready to go.
Also, since I no longer have the box for the accessories, you’ll have to settle for this really bad attempt at Photoshopping it in:
About the Mobile Suit
Here’s what the Gundam Wiki has to say about the Marsfour:
A variant of the Core Gundam docked with the Mars Armor. It specializes in close combat and is equipped with various melee weapons such as the Slash Blades. The various blades can be combined to form powerful large swords, allowing the Gunpla to deal with one-to-one-combat, one to many battle, and against enemies that are much larger. Acceleration devices are also built into the Mars Armor, greatly enhancing Marsfour Gundam's instantaneous force. With its nimble attacks and maneuvers, the Gunpla can slice through various enemies.
Similar to how the Plutine Gundam reminded me of a mobile suit version of Sailor Saturn, Marsfour feels like the mobile suit version of Sailor Mars:
It’s red and fire themed (and Mars themed of course). Not all of Planet Armors feel like their Sailor Moon equivalents, but when they do, they really do.
Weapons
It’s swords. The Marsfour has lots and lots of swords.
Oh, and an axe too.
In all seriousness though, let’s do some inventory.
First, we have a pair of identical blades called the Slash Blades. They can also combine into one single, even larger sword.
Then there is the “Heat Rev Sword”. This is a single large blade that can get red hot. It’s what the Marsfour is holding in its most iconic pose:
Then there is the Heat Rev Axe, which can be used separate, and can also attach to the Heat Rev Sword (you can see it in the photo above if you look close).
And even without its weapon set, the Marsfour is still packing heat. It has two shields on its wrists, which each have a set of fold out claws. Even when it’s on defense, it still goes on offense.
Appearances
Some of the Planet Armors show up multiple times in Build Divers Re:Rise. Others get one big appearance in the first half of the show, and another one in the second half. And some just get one big moment to shine. Without going through the entire show again, I can recall two episodes where the Marsfour appears.
The first is its debut in Episode 3. The BUILD DiVERS attempt to stop an enemy invasion by funneling them through a narrow passage so that Earthree Gundam can pick them off.
Things mostly go as planned, except for the fact that they missed one enemy mecha that was “knocked out” under some rubble, which then wakes up and starts going on a shooting spree.
Hiroto chooses to take this singular foe on using the Marsfour armor, mainly for two reasons. First, it’s acceleration devices allow it to move the enemy farther away from the villagers it was attacking. Second, it’s melee weapons would have a better chance of destroying it without causing its reactor to explode (thus harming the nearby village):
So first he bum rushes it, and once it’s a safe enough distance away, he cleaves it in half with the Heat Rev Sword:
It’s not the most exciting battle: I think it would have been better if it had been given a chance to take on multiple enemies at once. Nor does it really demonstrate what the armor is fully capable of. But it’s the closest thing it gets to a showcase episode.
The next time I recall seeing it is in Episode 9. The team is trying to defeat an amphibious mobile armor, and they decide the best way to do it is to slice it up like fish. Once it’s out of the water, Marsfour uses its blades to do the job:
There may be other appearances that I’m missing from later on in the show, but these are the two I can recall.
About the Real Type Core Gundam
This kit comes with a specially colored Core Gundam, which the box describes as “Real Type Colors”.
Real Type Colors are “A Thing” with Gunpla, and I don’t think I’ve ever explained it before.
Long ago, when Sunrise released the second Gundam Compilation movie, they put out a promotional poster by Kunio Okawara featuring the Gundam in an unusual color scheme:
Initially, this alternate colored Gundam only existed as part of this poster. But as they are wont to do, Bandai went ahead and fleshed it out. Dubbing it the Real Type color scheme, it eventually received an entry in MSV-R, which explained that this is how the Grandaddy Gundam appeared in Earth Federation training simulators.
It also received a model kit with some sick looking artwork:
Ever since then, they’ve released models of other mobile suits in their own Real Type color schemes:
There’s no real consistency to the color schemes, nor are they necessarily more realistic in nature. They tend to feature lots of greens, reds, and dark yellow/orange, though not always. I just tend to look at them as fun alternate colors, and leave it at that.
Now, I don’t remember the Core Gundam ever appearing in Re:RISE in its Real Type color scheme, just as I don’t remember seeing it appear in its Titans colors. But I could be wrong!
I thought it showed up during a flashback in Episode 9, but no, it was in its G-3 color scheme for that scene. So I’m pretty sure it’s just not a thing in-universe.