A lot is buried in our progress updates on SubscribeStar or in twitter posts D:, but we have documents available on our Discord.
The story mode will consist of 6 or 7 stages/zones with multiple routes/bosses, as well as event and side missions accessible via the world map.
There are experience levels, loot/shops for equipment, and will be a skill progression system that allows for customization of the player's available moveset/combos/active skills.
Equipment changes the visuals on the player character, but we're looking at a "phase shifter" slot that would effectively be a costume slot that overrides equipment visuals. Also a "wave shifter" slot that would allow the player to equip a color palette (similar to retro beat 'em ups). Wave and Phase Shifters would be loot/rewards like other equipment.