Re:birth is the name given to one of Dir En Grey's earliest songs. Unlike 藍紫色 and 刹那, Re:birth is one of the lesser known indies songs by the band.
It was never released in any form and there are only five confirmed live performances: On August 8, 1997, the second day of Album「MISSA」発売記念2days at 新宿 LOFT, on October 28 and 30 that year during CRUCIFY OF MARIA …TO "MISSA" あなたの『美的・発情・香』を呼び起こす, the following year on May 5 during 「楓」～if trans...～ Mechanism For Leave - Unknown...Despair...a Lost... ～裁きの血舞台～ and on August 3 during ～in the secret cradle～蝋蜥蜴と硝子蜂.
A live report from Dir En Grey's indies days 1997–98 lists this song as 新曲2 Shinkyoku, which means "New Song 2". 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 24 June 1998. Rebirth is the fourth track on that album, you can listen to it here.