After the Legendary Giant incident, several warriors from different time periods begin to appear in the Kingdom of Lacroa and fight each other. What at first looks like a battle of defense would later turn up to be a battle Knight Gundam has never seen before.
Tropes associated with SD Gundam Ultimate Battle are:
- Adaptational Villainy: The original RX-0 Full Armor Unicorn Gundam was just an upgrade to the RX-0 Unicorn Gundam used by protagonist Banagher Links. Full Armor Knight Unicorn Gundam, on the other hand, is a monstrous form Knight Unicorn Gundam turns into as the result of Red Majin Shamblo's possession.
- Big Bad Wannabe: At first it looks like Shikou Musha Sinanju is the main threat, since he leads a major army in the all-out free-for-all and is the one Knight Gundam and Unicorn Knight Gundam have a climatic battle with. In truth, he's just a major distraction. The real threat is Red Majin Shamblo, who took control of Knight Unicorn Gundam since before the events of Ultimate Battle and is the reason behind said events.
- Brainwashed and Crazy: Turns out the armor Knight Unicorn Gundam wears as Full Armor Knight Unicorn Gundam is actually Red Majin Shamblo, and he's possessing him.
- Canon Foreigner: Plenty of new characters introduced here have been made for the pre-established settings featured. These include, but are not limited to;
- Shikou Musha Sinanju and Tsukito Gundam for the SD Sengokuden continuity.
- Knight Unicorn Gundam and Crown Knight Gundam III for the SD Gundam Gaiden continuity. Both later became Immigrants in New Testament SD Gundam Gaiden: Saddrac Knight Saga.
- Composite Character: While Full Armor Knight Unicorn Gundam is of course based off of the RX-0 Full Armor Unicorn Gundam, said armor in question is actually Red Majin Shamblo, who's based off of the AMA-X7 Shamblo.
- Crisis Crossover: This works brings characters from the SD Sengokuden Series, the SD Gundam Gaiden Series, SD Command Chronicles, the Gundlander Series, SD Gundam Force, BB Senshi Sangokuden, and more together to face a common threat.
- Fighting Your Friend: Played for Laughs. In one side-story, the SDR cast decide to duke it out with each other. Why? To determine who the "main character" of their work is.
- Fully Absorbed Finale: The story of SD Gundam Seidan gets some proper closure and resolution here, after the original series was unceremoniously cancelled at two chapters.
- "I Know You're in There Somewhere" Fight: During the fight with Full Armor Knight Unicorn Gundam, Mikoshimaru tosses him a card to seal Red Majin Shamblo in, telling him to snap out of it.Mikoshimaru: If you are Unicorn, you'd know how to use this, right? Now, you are not Red Majin. Use your "true heart"!Full Armor Knight Unicorn Gundam: My...true heart...
- Man Behind the Man: It is eventually revealed that the events of Ultimate Battle are Knight Unicorn Gundam's doing, because he wants to turn Knight Gundam into a card to make himself a god. It is then revealed that the armor Knight Unicorn Gundam dons as Full Armor Unicorn Gundam is really Red Majin Shamblo controlling him, and has been doing so since the beginning.
- Spotlight-Stealing Crossover: While this is a crossover between SD Gundam as a whole, most of the focus is spent on the SD Gundam Gaiden Series. The story takes place in Lacroa, Knight Gundam is a major protagonist, and the events are triggered by a character from the setting (Well, a Canon Foreigner, but it more or less means the same thing).
- There Can Be Only One: Played for Laughs. SDR never really had a "main character", so its cast ends up fighting each other to see who the perfect candidate could be.