Board Thread:General Discussion/@comment-150.176.227.111-20140123171758/@comment-3250527-20140718020722

All Unique Skills are supposed to be the strongest within the game, even better than the "Extra Skills" that anyone can unlock. These Unique Skills are only given to ten players, as there are only ten of these said skills, so eight other players (aside from Heathcliff (Kayaba) and Kirito) can inherit these skills if the Sword Art Online game were to continue.

But digressing from that train of though, these ten skills are designed to be overpowered: Heathcliff (Kayaba) was able to stall the 50th Floor Boss by himself for 10 minutes (probably using the system assist) while Kirito was able to solo the Gleam Eyes (though he nearly died doing so).

It is highly presumed that Kayaba designed that only the nine players bearing the Unique Skills would stand before him on 100th Floor to decide the fate of the trapped players in SAO.

By all means, yes, Holy Sword is supposed to be the most OP, allowing the wielder to "freely switch between attack and defensive stances". Dual Blades allows its wielder to "attack at mach speeds", and I can possibly describe the other 4 known Unique Skills.... another discussion for another time...