Art Gallery  -  A special art gallery opens when you finish the game using any character. The contents of the art gallery are sketches of the characters you have used to finish the game.

Play as Damian  -  Finish the game in any mode (easy, normal or hard), and Damian, the sickly guy becomes selectable. At the character select screen go to the right of Popura. 

Play as Bristol and Bristol_D  -  Finish the game 5 times. At the character select screen, go to the right of Damian, Bristol and Bristol_D (the devil) becomes selectable. 

Extract Windows Bitmaps from the Groove-On Fight CD  -  Use the SSCG extractor and load the CD in your computer. Go to the part where the files are named Gal_**.bin. Change the extension to Gal_**.bit and then one-by-one extract them. There are more than 50 images worth 62.5 MB!