In response to your requests, the high-difficulty [Bitter Sweet] mode has been added. (It can be switched from the options)
In [Bitter Sweet] mode:
* Enemies' attack power, durability, and speed are increased, making battles more intense.
* New powerful enemies are added to certain stages.
* Clearing the Boss Rush stage in Bitter Sweet mode will unlock 6 new playable characters!
Defeat the incoming powerful enemies and challenge yourself to acquire new playable characters!
Additionally, various graphical and behavior-related bugs have been fixed (ver.1.4.8).