I'm sorry if it's not the place for it, but I have a question. Is it okay to use music from videogames since my game is 100% free ? I have already seen Liar Liar do the same with anime music so..?
Even if your game is free, it's not good to use copyrighted music. There are plenty of websites that offer free to use tracks.
I recommend these;
https://soundcloud.com/alcaknight most music here is available to freely use in VNs with credit
http://slos.biz/ for rules on usage, just click the top right corner "for English simply put", you are free to use so long as linked to http://sentive.net/ and they have a report form to fill in (they like to know what projects their music is in, that is all)
http://www.hmix.net/ of course credit