Endurance

Endurance is the original Quirk of Gigantomachia.

Description
Endurance provides the user the ability to convert their morale into physical energy and stamina. We see through Gigantomachia that the more excited he is, or the more driven he is to accomplishing a task, the stronger he becomes.

The Quirk acts as the crux to Gigantomachia's usefulness as a bodyguard, as his unending loyalty to his masters, first All For One then Tomura Shigaraki, gives him the motivation to please them at any cost, thus increasing his strength.

This natural sense of energy and stamina appears to also allow him to very easily be able to hold and utilize multiple Quirks at once, without being affected by the strain on the body or mind, or having to be remodeled like Tomura or the Nomu.

Weaknesses
The downsides are that, eventually, the user's energy can be worn out through a repeated onslaught of attacks. Also, due to Gigantomachia's nature of always needing to follow orders, when he is on standby waiting for a command, he becomes inactive and unable to properly assist, like when the Gunga Mountain Villa was initially attacked, and becomes significantly weaker, allowing him more susceptible to attacks, like Best Jeanist's binds.

Usage
While the Quirk is one that resides Gigantomachia as his natural state of mind, increasing his power when ordered to attack, we see the most obvious activation of it when Tomura first awakens, calling upon him to bring the rest of the League of Villains to his location. His eyes spark up, gaining a sudden increase in happiness to hear his master's voice, before barrelling off toward him while accomplishing his given task.

We see this again during the climax of the battle, where another simple command from Tomura is able to reignite his strength and allow him to resist and eventually break free of Best Jeanist's binds.