Well, I see that this has been answered a numerous amount of times, but if anyone STILL needs ideas about this, I know about it. I am 14 years old and I love anime, which is a highly popular japanese culture thing. What I recommend for music (individual songs):
-Come, by Amuro Namie
-Four Seasone, by Amuro Namie
-Shinjitsu no Uta, from the Best of Inuyasha
-My will, by Dream
-Fukai Mori, Do As Infinity
You can find all these on
http://www.ear-tweak.com/wind/-Tip taps tip, by halcalli
-Sanctuary, Utada Hikaru
-Simple and Clean, Utada Hikaru
-No touch Coke, Junior Dee (funny song)
-You, by Kazami
-Believe, by Tamaki Nami
-Michiyuki from Loveless
-Tsuki no curse from Loveless
-Any songs from FullMetal Alchemist are cute! ^_~
-Some songs from Naruto
AYUMI HAMASAKI is a good person too.
As for themes, I recommend Inuyasha, Naruto (getting very popular), Hellsing, Trigun, Wolf's Rain, Final Fantasy, Rurouni Kenshin, Kingdom Hearts,etc.
Ideas is a dress up thing-y, with Kimono's,set up a place in your house where they can drink tea with their sandals off! You can give the store that is making your cake a picture in advance for the top! Gifts can vary from Anime DvDs that you know they like and/or manga. Keychains, or small anime accessories always make me giggle with happiness.
You can also rent anime movies to show at night after they are all in their pajamas (if it is a sleepover).
Hope I was of some help! ^_~ Good luck!