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
Ultra Seven
Ultraman Taro
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:
Alien Baltan
Red King
EX Red King
Bullton
Gomora
EX Gomora
Alien Mephilas
Geronimon
Eleking
EX Eleking
Tyrant
EX Tyrant
EX Tyrant II
Kyrieloid
Chaos Kyrieloid
Waroga
Chaos Waroga
Chaosroid U
Chaosroid S
Chaosroid T
Neo Chaos Darkness
Neo Chaos Darkness II
Source: Wikipedia, "Ultraman Fighting Evolution Rebirth", available under the CC-BY-SA License.