Eyyyyyy, I figured it out! I emailed the creator of it and he sent me the song!!
Here's the song name if you were wondering...
Song Name:Trauma
Author: Ayumi Hamasaki
In the Custom Ouendan BETA, I was just wondering what the song was in it...
It's so freakin' catchy!! I must know! ^-^
*edit*
Here's the link if you were wondering...
http://gbatemp.net/index.php?download=804