I do not own 2nd# myself, but my cousin who I introduced to Project Diva does. From what I've heard it has to do with getting the Extend Modules in 2nd through the PSN store? Since she lives very far away I can't figure it out myself and trying to skype-call and do it without set steps is too difficult. I don't know anything about using the Japanese PSN store on the PSP so... Is that code what I think it is or is it for something else? Since I don't really know and this idea is only based off of mentions about it that I've seen in the forums. How would the code be redeemed? Would the package be usable even if the PSP is logged into a non-Japanese account afterwards? All help would be appreciated!
Yes, it's about getting the Extend modules in 2nd/# as DLC. You'll need to use the code in Japan PSN since the DLC doesn't exist in US PSN. You can redeem it using the PSN app on the PSP itself, but it's probably possible to redeem it by web. The DLC is still usable even if you login to the Japan PSN since it's already saved on the Memory Stick or even on the PSP GO's internal memory, but it's best to just save it on the Memory Stick for faster loading.
Create a japanese PSN account or login with an existing japanese PSN account on your PSP and go to the store. Go to the symbol for code redeemtion and enter the code which is in the game case. Now you should see the DLC pack to get the extend modules in 2nd# and download it. There are several tutorials on the internet how to create an account for the japanese PSN and how to navigate in the japanese PSN store. That's how I got my DLCs for 2nd, extend and 2nd#. :)