Played the game for a few hours and here's the feedback i would like to say;
The flow of the game is nice, there's a lot of things going on but not to the point of being overwhelming, battles are a fair challenge. However it's with the battles i began having issues with how the game plays;
Skills both passive and normals are far too one dimensional with all characters, what i mean by this is the fact that most skills have a singular action trough out all rarities, making the advantage of having higher rarity character simply being "higher stats" which to an extent defeats the point of them being harder to pull.
Same can be said for passive skills, a good portion of them are bland and barely make a difference in gameplay if at all, once again defeating the point of character rarities to an extent, after all what's the point of farming to get a Rank 1 character when they bring almost nothing to the table other than higher stats?
As a suggestion; give higher rarity characters multiple effects on a skill, for example "Heavy Slash - deals moderate physical damage to 1 enemy and buffs own defence by 25% for 1 turn". Same thing can be applied to passive skills, example "Heaven's Door - Buffs all allies atk by 10% for the first 3 turns in battle; Heals 5% of own HP for the first 5 turns". Skills like this on higher rarity characters would give a much better reason to summon for them since they will be much more impactful in battle.
For my second and last feedback for battles, it's definitely the UI. It works fine for the most part but some information could definitely use a bit more highlighting, what i mean by this is that the "target" indication is rather small and not very eye catching, so on the first few battles i was rather confused on who i was actually targeting. While i did get used to it overtime, i think it still is something worth keeping a note of.
Overhaul i see a lot of potential in this project of yours and i hope at least some parts of my rambling can be of use to you. Good luck on your future projects!