All of the locked art in the gallery is gotten by meeting certain goals. The following list will tell you which characters you need to choose and which of the games do you need to beat with them

Unlockable	How to Unlock
Art #101 - #102	Beat Vampire Savior with Q-Bee
Art #103 - #104	Beat Vampire Savior with Lilith
Art #110	Beat Vampire Hunter 2 with Gallon
Art #111	Beat Vampire Hunter 2 with Aulbath
Art #112	Beat Vampire Hunter 2 with Sasquatch
Art #113 - #114	Beat Vampire Hunter 2 with Oboro
Art #117	Beat Vampire Savior 2 with Donovan
Art #118	Beat Vampire Savior 2 with Phobos
Art #119	Beat Vampire Savior 2 with Pyron
Art #120	Beat Vampire Savior 2 with Oboro
Art #121 - #144	Beat Vampire Savior Arrange with Shadow
Art #14 - #25	Beat Vampire with each character in the game
Art #145 - #168	Beat Vampire Hunter 2 Arrange with Marionette
Art #169 - #192	Beat Vampire Savior 2 Arrange with Marionette
Art #27 - #30	Beat Vampire Savior Arrange with Dee
Art #46 - #59	Beat Vampire Hunter with each character in the game
Art #61 - #79	Beat Vampire Hunter 2 Arrange with Dee
Art #97 - #98	Beat Vampire Savior with Jedah
Art #99 - #100	Beat Vampire Savior with Bulleta