Well, Fantasy Zone and Space Harrier take place in the same... I'm presuming an area of space. Putting the Valdi System in the Fantasy Zone could be a maybe.
But here's my "revised Ristar" story so far.
- The Valdi System consist of eight planets. (I'm not sure where Planet Terra or Timu fit into it, I don't remember these planets.) Each planet is inhabited by a unique dominant species, such as Planet Flora which is inhabited by goblin-like people.
- I've yet to decide the currency of the Valdi System, but I imagine something of the like of Tiffany Yellow Diamonds being the common coinage of sorts. (Though in a hypothetical remake of Ristar, I can't really imagine much use for currency, let alone a point-system.).
- At some point in history, the Valdi System had something a kin to "Star Warriors", an organization that consist of various mix of aliens that serve as galactic defenders of the Valdi System who fought against some great threat. While they have won the war, the numbers greatly dwindled.
- Alistar was the greatest of the Star Warriors, so great he won the favour of Oruto, the Star Goddess. Oruto fell in love with the mortal hero.
- After a time of peace, a new invader arrives to the Valdi System, a pirate named Kaiser Greedy who sought to establish a galactic empire. "Planet Greedy" being a ship of sort.
- What makes Kaiser Greedy so powerful, as well as his name sake, is that his planet/ship is powered by a black hole! Kaiser Greedy draws power from it, able to create and control "mini black holes" which he uses to attack.
- Kaiser Greedy has the unique power to create lifeforms from dark matter. He turns them into Black Orbs.
- Black Orbs are an extremely adaptive and transformative enemy. "Orblets" being somewhat of a protoform of black orb creatures, but when black ob creatures find themselves in an alien ecosystem, they quickly transform and adapt to their surroundings.
- Kaiser Greedy's henchmen are Inonis and Uranim. Inonis is scientist and engineer, able creating machines for Greedy, maintaining his armour and creating weapons powered by dark matter or monsters from black orb creatures. Uranim is the muscles, a cyborg created by Inonis and powered by a black orb creature.
- With Alistar, the last of the legendary heroes missing, Oruto awaken their son, Ristar, to find him and to save the Valdi System.
A black hole as a power source?
I guess this is a Schwarzschild black hole kind.
The one that has no electric charge or angular momentum.
The neutral one that doesn't spin.