This is JRPG with battle system inspired by trading card game (there's PVP mode for time-killing). The characters (with Solomon's Goetic demons theme) are very varied in both appearances(human and 'demon' form), personality, and playstyle. All start from 1-star and can be evolved to 6-star. So you get to choose who to evolve based on their ability rather than rarities. Even story units can hold their own ground. The same goes to the event freebies.
Non-chibi 3D models are well-made (some motions are really fun to look at). Music is great. You get to hear at least 1 new track or new remixed version every month
Recommend to anyone who loves TCG/RPG hybrid. The downside is you need the Japanese language knowledge (or some sort of JRPG gamer's memory) given the game's complexity. the system UI can use more work (they're improving) and character design can feel old-fashioned(says, 90's shounen manga). I still can't excuse the main protagonist's outfit but the game is fun enough for you to look past that (and get used to it, sort of). They're also not shy away from showing some disturbing graphic violence (self-stabbing is one of the mildest examples). They were done in a somewhat artistic way (no gore) but unsettlingness can be too much for a sensitive person. Rates aren't really bad (unit rates are normally 5% and boosted to 10% in Sabbath banner) but you don't get to roll much often (especially after finishing main story chapter3). In your unluckiest month, the event freebie will be the only new unit you'll get.
(2020 update) The game has added more endgame stuff so veterans will have something to go after. Most notably 'treasures', an equippable accessory that gives character more benefit. Exclusive treasures are also introduced to buff older characters ranged from minor change to complete overhaul. While I'm not active on more challenge-minded mode like 心深圏 (hunting boss with twist) and legendary megido quest, it's still nice to see high-skill players go wild.
Raid battle is nice little fun event where you can see other players (and their funny comments). And music....you can finally change home music! (accessible via setting menu). Yorisaki Ryo, the composer consistantly makes a new track so it's good to hear some of those tracks in-game whenever you want. The game has gotten so much popularity that it's hard to imagine they had a "should we shut this down" meeting in 2018. DeNA and Media.Vision now have to face a challenge of meeting user's higher expectation. I hope they keep doing better. The game isn't without flaw, mistake, or questionable decision, but they're alwasy trying to deliver and I'm happy to witness their journey.
For anyone starting this game in 2020 onward, what I said in 2018 still applies. But it gotten better now that some essiential event units are always available as a permanent event (locating on lower right corner of event entrance). This is the game that reward learning and utilizing your units as well as a long term investment. Wish you best luck on this wild, puzzling yet very fun game :D
(Lowkey +1 point to the story since newer chapters kept getting better than the last while also giving pre-existing cast more depth. If they can stop rewriting their lore for another year I'll probably come back and add another +1, Not FGO level of epicness and expandability but it's fun to read and think about)