Aside from the gear option, is there a reason it has to be Fine's fireball? He calls it "fireball" here, but Mary's "purgatory flame" is also a long ranged fireball attack, and he can still copy her abilities. Unless there's something in this series that says you actually must say the skill name when using it, he could just be using hers and lying about it (though he previously said Mary's copy only lasted ~5 minutes now, maybe they did some funky play pre-match to make her hate him more, or something), in a decent amount of series spells can still cast without chanting, they're just weaker (and if he's really just using it as distracting covering fire for Fine's melee attacks, he doesn't care how weak it really is).
But since Fine's bit here is based on skill-effecting items, I figure it's probably just an item for Mikagami here too.