Ultimatum or Last Resort(最後の手段, Saigo no shudan, American translation) is a very powerful combat ability system in conjunction of the Limit Break System in Final Fantasy and Kingdom Hearts series. Ultimatum can only be used during Ultima Mode, using Ultimatum will instantaneously ends Ultima Mode, hence the ultimatum part.
Each character possesses their own Ultimatum. Some other enemies, namely the protagonists may also possesses their own Ultimatum, in conjunction of they also have Metamemory Grids. In order to activate Ultima Mode, the character must fill up their Smash Gauge. To perform the character's Ultimatum, the player must engage in various button selecting similar commands to the EX Burst in Dissidia/012 Final Fantasy.
Unlike other more common abilities, Ultimatum's Attack Power is based on the character's Level, and mainly their Base stat. When using an Ultimatum, time is be greatly slowed(including in the Gameplay Time). When damaging an enemy using Ultimatum, there are no damage indicators, so they player might've think of them as rather weird. Almost all Ultimatum's damage cannot break the damage limit, since most of them deals damage in barrages, they rely on how many combos the character can exploit. However, Ultimatums that only does one instance of damage can break the damage limit, and does not rely on quantities.