新曲2 is one of the three songs by Dir En Grey that were never properly released and only performed live in their indies era from 1997 to 1998. The other two are 藍紫色 and 刹那. Unlike those, this song never received an official name, but it's also known as Re:birth.
It was never released in any form and there are only five confirmed live performances: On August 8 and October 28 and 30, 1997, as well as on May 5 and August 3, 1998. It is also mentioned in FOOL'S MATE #198 (April 1998), where Kyo explains that 新曲2 and 新曲5 were not finished yet and didn't receive proper names. 新曲5 would later be known as 藍紫色.
It is unknown where the name "Re:birth" comes from, but it's likely a fake name and could be inspired by "Rebirth", a song by the Japanese rock band Eliphas Levi. They were active during Dir En Grey's early days and released an album called リデルの赤い書物 (Rideru no Akai Makimono) on June 24, 1998. Rebirth is the fourth track on that album, you can listen to it here.