Ultraman Fighting Evolution Rebirth is the 4th game in the Ultraman Fighting Evolution series.
Its Story Mode involves Alien Mephilas launching a massive invasion using EX monsters (more powerful versions of the originals) and sending three 'Chaosroids' (dark versions of Ultraman, Ultraseven, and Ultraman Taro) to the Land of Light. Eventually, Mephiles fuses with his final monster, Neo Chaos Darkness. With the combined effort between Cosmos and the other Ultras, they managed to defeat him and stop his invasion.
List of Ultramen:
Ultraman Tiga (Includes Multi Type, Sky Type, and Power Type)
Ultraman Gaia (Includes V2 and Supreme Version)
Ultraman Agul (V2)
Ultraman Cosmos (Includes Luna Mode, Corona Mode, and Eclipse Mode)
List of Monsters and Fake Ultramen:
EX Red King
EX Tyrant II
Neo Chaos Darkness
Neo Chaos Darkness II
Source: Wikipedia, "Ultraman Fighting Evolution Rebirth", available under the CC-BY-SA License.