Unlock More Characters
Play survival mode using the 2 enemy characters in the upper right character
selection menu to unlock hidden fighters (such as Ultraman Noah). Play the
character in the bottom of the middle row (the scorpion like monster) to unlock
the 3rd Nexus.

Play Deumantis
You may normally play as the 3rd Deumantis after you are defeated. Clear the
game once and you will get the option to choose between the 2 characters.

PS2 Cheats for Ultraman Nexus

Ultraman Nexus cheat codes

Ultraman Nexus cheats