You either need to lose or surrender using the option in the menu during Aeren's stage to unlock it. Aeren's stage is the one where you play as him the first time.
Thank you so much Red, finally got the scene x All scenes are complete. So after Dragon World, which world will you update next and when?
For now, we're focused on doing some very important reworks to base systems. After that, we want to progress the main story a bit ;)
The next planned world, however, is called Kogetsu City and it's modern world
