Secret Area
Once you complete the game by defeating the final boss, wait until the credits roll and the title screen appears. There should be a star next to 'continue'. When you continue the game, it will continue from the spot where you last saved as usual, but you will now be allowed access to the Secret Area, which is located in the Ura-Internet square. You can only get there by plugging into the computer under the hot springs. You will need 100 standard chip entries in your library to enter.

Secret Boss
After you complete the Secret Area by defeating Serenade, use the Bug Trader at least 30 times, then leave the internet. When your eturn to the Bug Trader, Forte will appear, fused with Gospel, and attack you. If you defeat him, you will get the Forte chip.

SP navis
After obtaining five stars, highlight Continue at the title screen, hold left, and input this code:

RRLRLRLL

The stars should move closer together. You can now find and fight the SP navis