Ring Suzune and Lui Hibiki (Unreleased Vocaloids; 2011-2012)
VOCALOID is a voice synthesizing application that has been sold commercially since 2004; like text to speech, but with singing. The most famous VOCALOID is Hatsune Miku, with dozens of other Vocaloid characters that exist beyond her.
Ring Suzune and Lui Hibiki were potential VOCALOIDS announced for the VOCALOID3 engine during its pre-release promotions. A release date of December 12, 2011 was initially confirmed, Ring and Lui were not released on that date. It is now unknown when or if they will ever be released. In 2012, VocaNext picked up Ring's voicebank to continue development but not Lui's, perhaps because female banks have a tendency to sell better, and nothing was heard about the development of Lui from that point forward. It is unknown if there was even a voice actor chosen for him, let alone a finished voicebank for the software's development.
Ring Found And Lost Again
In February 2012, a beta version of Ring Suzune's voicebank was offered to the participants of "Vocaloid Network", a small-scale fan event took place on March 11, 2012. As the number of fan groups which participated the event was only 19, it is considered that only a small number of people received the beta copy, though it was sent to all those interested. However, trial use of the beta version was limited to a month, meaning after a month, her software was once again lost.
In late 2013, the VocaNext website became inaccessible making the status of Ring, as well as Lui Hibiki, unknown.
In late September 2014, a message was sent to PowerFX asking if they could resume the Ring and Lui project. PowerFX replied saying that they have already attempted to resume the project. They had contacted YAMAHA, but the company said that a release was not possible. Other companies have not yet been asked or have not revealed their curiosity in public.
The songs linked below are the only known mixes made using Ring's official demo. There are several mixes on YouTube with a synthetic voice said to be Lui's, but none are confirmed to be legitimate.
Edit: Contradictory to previous reports, Vocanext's site continued to exist until at least January 2015 (warning: site contained some NSFW content), Their layout at that point had no mention of Ring Suzune; whereas, their previous layout promoted her on a huge "in your face" banner.