Ruinous Scimitar

This faintly glowing blade is warm to the touch.
When you successfully hit an enemy with this scimitar, you may choose one effect: (a) Gain 1
charge; (b) expend all stored charges, dealing 2
fire damage for each charge.
If you do not hit an enemy on your turn, the
scimitar loses 1 charge. The scimitar can have up
to 7 charges. If you expend all 7 charges at once,
a fireball (as the spell) detonates on the target
(1/SR).