I dunno exactly which song unlocks which one, but I unlocked mine for purchase in the store by just completing songs on Normal and Hard, Rin, Len, Luka, and I think Kaito and Meiko are some of the first one's you can unlock.
--- Meta-Decks in Yu-Gi-Oh have ruined the fun. Non-Meta-Decks FTW!.
not themes, actual character rooms... i unlocked luka and len's rooms i think sakine meiko's room as well... i unlocked rin room on my friend's game... i forget the songs... unless it goes by completion?... not sure...
Doh...never mind. XD Looks like I already unlocked them but then I have to buy them in the shop for 20000 points each. Press the R button in the Room submenu to see the room theme list.
2) Imperial Court (Clear all songs on Easy or better) 6) Japanese Castle (Clear Fanta - DSLR Remix on Normal) 7) School House (Clear Miku Miku ni siteageru on Normal) 8) Cherry Blossom (Clear the last song on Normal)