Aaaaaah yes!!! Some Vocaloid fans!! :D The song inspired me the game so I asked the producer if I could use it in the game's credits and she/he said yes!! :D I was so happy!
Thank you so much for your lovely feedback on the game and your enthusiasm! It's going to be a short game but yeah, I hope you'll have fun finding the parts inspired by the song... ;)
Regarding the game, I still don't know if it's going to be free or not, my first intention was to make a free game but we'll see how it goes. \(^__^)/ And the best thing you could do to help the game is exactly what you did: showing your love for it and encourage me to do my best! So thank you!