Unlock Gunvolt-Only hidden challenge mode.
- Complete true ending, which then unlocks “Primal Dragon” Image Pulse. This makes you start a level as Gunvolt instead of Kirin.
- Equip the image pulse, and beat 3 levels WITHOUT going back to Kirin. You will get an SS rank for the level for doing this.
3 best levels for this are probably Holy Night XIII, Holy Night XIII (Hard Mode), and Mystic Mist.
Arc Chain is your friend, tag multiple enemies before using it for higher score and more fetters energy.
Flash field the boss once you reach them since its safer then getting close.