This technique is a variation of Tsukuyomi, a high level genjutsu. The user transforms the Tsukuyomi into a barrier that slows the opponent down. This does not happen physically but rather mentally. It makes the opponent think they are being held back by a barrier. While using this technique, Itachi's health and chakra slowly go down. If Itachi uses this technique when his health bar is low, he could finish himself off.