Their everyday life is shattered one day, when they are suddenly dragged down into a mysterious world that they'll soon learn is the underworld, by a revenant called Anamnesis. The natural order of things in the underworld is that spirits make their way down towards the Gear of Renewal, which absorbs their souls and prepares them to eventually be reincarnated. However, some dead people have too strong a desire to keep on living, and become 'revenants' who usually try to revive themselves by absorbing other souls. Already-deceased souls on their way to the Gear are an okay source of energy, but the best source of power for revenants are the still-living. And so, Anamnesis pulled Rei and Mirai down still living into the underworld. When Mirai is in trouble, Rei finds a hidden power inside herself - a guardian spirit that offers her power, which she accepts to protect Mirai.
Mirai is dead, yes, but her spirit has only just begun wandering toward the Gear of Renewal. If Rei can both find Mirai's spirit and also overcome a bunch of trials set up by Mephis and Pheles, giving them the energy she collects from them, then they promise to use their power to resurrect Mirai. Accepting their terms, Rei becomes a 'proxy' for them, able to enter and leave the underworld at will, and is set on her mission of overcoming trials and finding Mirai's spirit before it reaches the Gear.
That about sums up the setting without getting too spoilery. I have to admit, I was really, really skeptical of the whole game's story from the beginning. From the name 'Crystar', to game mechanics based around tears, to having someone from Key on staff, I was expecting a whole bunch of over the top 'trying way too hard to be sad and make you cry' stuff. And while I do have some complaints with the story (especially the ending I thought was really weak), it wasn't what I was expecting. There's no barrage of 'this should be making you bawl your eyes out' substories, just a bunch of sad stuff that adds up to a general mood of despair. By the time I got to the mid-game or so, I was really hooked and wanting to see what would happen next every chapter.
The biggest issue, though, is that the enemies are just too tanky. They're health sponges. Both the normal enemies and the bosses. This is a real shame, because there's a decent equipment combining/strengthening system where you can boost your gear using drops from enemies, but I didn't get to use it all that much because I couldn't be bothered farming the needlessly spongey normal enemies. Once you've figured out a particular normal enemy's attack pattern, if you're paying attention you're no longer in any danger of dying, but you still have to whittle down its HP agonizingly slowly anyway.
Speaking of the bosses though, I thought they were decent. Most of them start off with only a few attack patterns at the start of the fight, but as their health gets lower, they gain more that you need to watch out for. You can spend the first part of each boss fight cycling through your 4 characters and filling their special gauges while memorizing the initial patterns, and then when more attack patterns come at you later, maybe you can brute force through some of them with your special gauge if you're not good enough to dodge everything. It becomes a bit repetitive in later chapters because you face many of the same bosses several times, but at least the first time through was pretty fun.
The music for this game was also above-average, with a few tracks in particular that I really liked. And as you've probably noticed from the screenshots so far, it's a very stylish game. From the opening animated by Shaft, to the drawings by Hajime Ueda sprinkled throughout, to the character designs by ryuuichi and ntny, it's got an aesthetic that came together well and I really liked.
The playtime for me was about 24 hours. It's not a long game, and I wonder if that's part of the reason they made the enemies so sturdy, to pad it a bit, but I'd rather it had been a short 18 hour game that I enjoyed all aspects of, instead of 24 hours that included a bunch of slowly whittling down health bars in between the story I wanted to see the next chapter of.
Anyway, if you're wondering if you should play it or not, I guess it mostly comes down to if you like the game's aesthetic. That's the main thing it has going for it, and if you like Key writing then that would be a plus as well (for better or worse, it's Key until the very end).
Thanks for reading, here's to a fun 2019!