Give Sega credit - they could have wrote off Crystal Warriors as a hasty and failed attempt at a Fire Emblem clone and never thought of it again, but they instead put in some elbow grease and gave it a sequel that is much improved. Too bad this one never made it out of Japan.
I'm honestly not sure if the story of the previous game ties into this one in any way, but it's clearly by the same team and uses the same basic gameplay style. It's fundamentally a clone of Fire Emblem, what with the limited between-battle activities, the lack of grinding and the perma-death. But as with the prequel, the sword-axe-lance triangle of FE is replaced by fire-wind-water, with earth standing alone as a middlin' class that isn't particularly good or bad against any other.
The story also centers around magical crystals of the elements, this time the four Royal Stones that guard the land in some way or another. Our main character Eva is a military commander falsely accused of deserting her post. It seems the punishment for this is exile, which doesn't sound so bad. Until you learn that this country's version of "exile" is to strap you to a cross and drop you off a cliff into the ocean.
Eva inexplicably survives, however, and the story picks up half a year later as she's protecting some village along with a ragtag band of skips and skallywags. Various contrivances will of course send her off to war against the Evil Empire violently gathering up all the Royal Stones for nefarious purposes. It's as stock a plot as you can get for a '90s JRPG (and largely recycled from the first game), but Royal Stone does surprise by being just a bit darker than the usual console fare, with sympathetic characters dying badly as the Evil Empire fails to pull the usual punches that more kid-friendly stories do. I mean, don't expect early-season Game of Thrones or anything, but it doesn't hew strictly to Final Fantasy Rules either.
As with the prequel, you progress through a linear series of 16 battles, with little breaks in villages in between to chat up some NPCs and do some shopping. A lot of little tweaks really improve the formula here, however. There's more story and characterization - text on the battlefield and in-game cutscenes (including flashbacks), and more detailed plot sequences in the towns in between battles. As far as actual gameplay goes, everything is also a bit smoother. The game volunteers more information up front without having to click through multiple menus, and there are more menu commands for convenience.
Gold is also in much more generous supply, eliminating the biggest headache from the first game - spending too much of your limited funds on the wrong thing during a town sequence and being screwed for the rest of the game. If you diligently kill all the enemies thrown at you, you'll have more than enough money to buy everything you need and still have a nice retirement fund left over at the final map.
In fact, the one big criticism you can levy against this one is that it's too easy, a sharp change from the original. If you are at all familiar with SRPG conventions and have even a basic head for strategy, you'll probably steamroll right through this game with little trouble. Enemies tend to move in same-element packs in a predictable way, and will wander right into your defensive traps over and over. The only time the game gets challenging is a couple of cheap moments where enemy reinforcements are popped out unexpectedly close to a town you have to defend.
The other big improvement here is aesthetic - if you want to see 8-bit pixel art taken to its heights, this is a game to have in your library. It looks better than quite a few Genesis (and even SNES) games I can think of.
Royal Stone is still wanting for a few things, but this is still a significant improvement over the first game and also one of the (very infrequent) gems of the Game Gear library.