Go to the Extras menu of the DVD (that's included with the game) for secrets that relate to the game.
Secret Keywords
Here are secret keywords from the OVA and other DVD materials. You must use them in Server Sigma.
Barking Hotblooded 500-Lohan
Unusual Ghostly Remnant
Abrasive False Tradgedy
Sacred Noisy Ringing-Ears
Ancient Destroyed Battlefield
Hint: Virus Cores
Here is a list of which virus cores you can get from which monsters by data draining them. (Note: There are always exceptions.)
Delta and Theta servers:
small monsters - virus core A
medium monsters - virus core B
large monsters - virus core C
Lambda server:
small monsters - virus core D
medium monsters - virus core E
large monsters - virus core F
Sigma server:
small monster - virus core G
medium monster - virus core H
large monster - virus core I