Lightning Rejuvenators in Subquest 4
If I remember correctly (i have a nasty habit of uninstalling games i completed), as long as you have the green effect (was it charged? It works like the freezing or burning effect), the Lightning Rejuvenator absorbs all damage dealt by the character with said effect. You should clear it with one of Ross's skills then dish damage.
C'mon, who hasn't stocked in items in RPGs like a madman? I know I do.