With Tenacity equipped, the Special Gauge gradually fills anytime the wearer's team has more inactive (waiting to respawn, or disconnected) players than the enemy team. The rate at which the Gauge is filled is dependent on how many teammates are inactive. The effect ends when the team's number of active teammates is equal or greater to that of the enemy team. This ability is restricted to headgear as a main ability, and cannot be rolled as a sub ability.
This ability is found as the main ability only on headgear, so other abilities found only on headgear are mutually exclusive with it; in other words players cannot have them together. These abilities are Comeback, Last-Ditch Effort, and Opening Gambit.
Splatoon
As of 2.6.0, the total time it takes to fill the Special Gauge without covering ground with ink: