How to unlock the two boss characters

[Louco Diamante]

I finished story mode and only unlocked one of the game's two bosses. How do I unlock the other character?

[Louco Diamante]

EDIT: After closing the game and opening it again, the boss that had been unlocked returned to the locked state.

[Ilay]

Unlock other by beating arcade with any character. I am not sure, if story should be beaten first for this to work.
For me characters are being "locked back" after every update.
Upd: I tried to unlock characters before beating story mode - did not work. It seems that you need to beat story first and arcade after this to unlock.