Nihilism

Nihilism is a recurring character motivation in the Final Fantasy series, detailing that nothing truly matters. It is often utilized by the villains of the franchise to justify their actions. In some cases, the heroes will refute the villains' motives with their own experiences.

Final Fantasy V
The main villain Exdeath, shortly after being accidentally sucked into the Void during his final confrontation with the Warriors of Light, devolved into nihilism upon turning into Neo-Exdeath, proclaiming that he will continue to destroy until there was nothing left to destroy, and only then would he cease to exist.

Final Fantasy VI
The main villain Kefka Palazzo, when confronting the Returners in the climax of the game atop his tower, informed them of his motives of destruction by stating that life and creation was ultimately meaningless due to their ending anyways. When the Returners refute his claims by citing personal examples of finding positives in the ruined world, Kefka ended up going berserk and raging that he'll destroy everything. He later reiterated his nihilistic beliefs when confronting the party in his God of Magic form.

Final Fantasy XIII
Although not explicitly referred to as such in the game itself, Barthandelus was labeled as nihilistic in his motivations in the description for the Fighting Fate DLC in Theatrhythm: Final Fantasy.

Dissida Final Fantasy & Dissidia 012 Final Fantasy
As in their original games, Exdeath and Kefka Palazzo were depicted as being nihilistic, although their exact views differed, especially in Shade Impulse: Exdeath's main motivation for his nihilism was to die, and was glad to finally be killed when defeated by Bartz. Kefka, likewise, was largely melancholy when revealing his nihilistic views upon being defeated by Terra Branford, causing her to speculate that he was motivated by a broken heart. The Emperor also expressed disgust towards Kefka's nihilism when Garland commented that Mateus was not different in terms of scheming to Kefka.

Theatrhythm: Final Fantasy
The description for the DLC song Fighting Fate from Final Fantasy XIII alluded to Barthandelus as being nihilistic in his motives.