I was planning on just stealing the Finishing Move maneuver's mechanics. :V
3d6 if at full, 5d6 if less than full, and 10d6 if half or below.
+1d6 per other sentai using it with you (max +4d6), +2d6/sentai for less than full, and +4d6/sentai if at half or less.
11th level ability, for reference.