Here are the level codes.

They have to be typed on the main menu.

Level B : EARTHIAN
Level C : KENICHI
Level D : INOKUMA
Level E : BURAI
Level F : BADMAN
Level G : NETWORK
Level H : YOKOHAMA
Level I : EXACT
Level J : X68000
Level K : TURRICAN
Level L : REDMOON
Level M : CAMPAIGN
Level N : MEGAMAN
Level O : SYVALION
Level P : FMTOWNS
Level Q : CHIERIE
Level R : GAMERION
Level S : ZAWAS
Level T : ROBOTECH
Level U : POPULOUS