Fusion Bolt inflicts damage. The base power of Fusion Bolt will double
if another Pokémon uses Fusion Flare immediately before the Pokémon
using Fusion Bolt, but only during that use.
That is the description of Fusion (Bolt/Flare). By this I tested it on the Grimsely's Scrafty. I did this 2 times. After looking at the results, It is clear that I am famous (You have written my username up there) and that it is only powered up for 2 uses.
So If Reshi used F-Flare, it would deal BP of 100, and then if Zek used F-Bolt, it would have a BP of 200. Then this restarts again.