If my opponent has Spiritomb with the "Fettered in Misfortune" Ability in play, does attaching a Fusion Strike Energy to my Genesect V allow it to use its "Fusion Strike System" Ability or not?
Fusion Strike Energy protects Genesect V from the effect of Fettered in Misfortune, so yes it would be able to use its Fusion Strike System Ability.
Source: TPCi Rules Team (2023-07-13)

Relevant cards

Note: All applicable cards may not be listed below.
SV2_89
SV2_89
SWSH8_185
SWSH8_185
SWSH8_244
SWSH8_244