Key points
General information
BulletWitchLangauge
<path-to-game>\savedata
BulletWitchSaveData
BulletWitchSystem
BulletWitchRecord
Issue does not arise if the game detects a gamepad plugged into the system. Keyboard and mouse can still be used to play the game as long as a gamepad is present. This may be complicated on Windows 7 and earlier due to Xinput support issues.
devmgmt.msc
~/.steam/steam/userdata/<user-id>/696180/