Multi-Dimension Bomb (
In BlazBlue: Chronophantasma, Kokonoe claimed to have implanted the device in Ragna's left arm. After activation, it's set to explode if he wanders a set distance away from Celica, so he always has to stay near her. If the two were to become separated from one another, then the bomb would detonate, killing Ragna and a great many others in the vicinity.
In reality, the MD Bomb was never implanted in Ragna's left hand. Instead, she installed a Noise Canceler in order to gather data. Kokonoe simply lied about the MD Bomb to keep Ragna constantly near Celica and under her influence.