This is my fourth favorite Honeyworks song as well as one of my favorite Rin and Len duets so far. Classic. It's an old one with some poor tuning, but the song itself has really shaped the VOCALOID industry and its personification of the libraries.
This is one of my favorite Regulus songs as well as one of my favorite Megurine Luka songs. I remember listening to this just a few hours after it was released.