Complete the game on Hard difficulty with a rank of A or higher. Then at the screen that has the Tecmo logo, hold L2 until the Tecmo logo screen disappears. Rygar's Diskarmor will resemble a hamburger.
Sushiarmor
Complete the game on Legendary difficulty with a rank of A or higher. At the Tecmo logo screen, hold L1+L2 until the Tecmo logo screen disappears. Rygar's Diskarmor will resemble a plate of sushi.
Pizzarmor
Complete the game. After completing the game, press L1 at the Tecmo screen to use it.
Guitarmor
Reach the 30th basement floor of the Necromandio Cave and break the Silver Cask to be able to use the code to play with the Guitarmor. At the Tecmo logo screen, hold R1 until the Tecmo logo screen disappears. Rygar's Diskarmor will resemble a guitar.
Udonarmor
Reach the 30th basement level in Necromandio Cave and break the Silver Cask to enable the code to play with the Udonarmor. At the Tecmo logo screen, hold R1+R2 until the Tecmo screen logo disappears. Rygar's Diskarmor will resemble a bowl of Udon.
Rollerarmor
Reach the 30th basement level of the Necromandio Cave and break the Silver Cask to be able to use the code to play with the Rollerarmor. At the Tecmo logo screen, hold R2 until the screen disappears. Rygar's Diskarmor will resemble an enemy called Roller.