A Critical Down クリティカル・ダウン, kuritikaru daun?) is a phenomenon that occurs occasionally during a Dive, in which the Reyvateil rejects the Diver and expels him or her from her Cosmosphere. However, this also has more serious consequences, as in cases of extreme incompatibility, the H-Waves of the people involved will be completely unable to synchronize with each other and the end result will be that the H-Waves of the Diver will be absorbed (devoured) by the H-Waves of the Reyvateil, destroying his/her mind and leaving him/her as a vegetable.