3rd Story CD Lost is the third doujin album released by Sound Horizon on December 30th, 2003. It contains 12 tracks and 11 bonus tracks and was released at the 63rd Comic Market. The album retailed for ¥1,500 and was the first doujin release to feature 霜月はるか (Haruka Shimotsuki) and Jimang, who became staples of later Sound Horizon releases. 5 of the WAV files are compiled as a Windows Vocal Collection so fans can replace normal Windows sounds with Sound Horizon ones. These files can only be played using a computer using a collection of HTML files. These files are the first to feature the character Picomari☆. This is the first work to refer to horizons using numbers.