Its utilization requires removal of its restraints, after which the user has to pierce the target with its blade. At that point death is placed in the target's mind. In the instance that placing death in the opponent's mind is impossible, the blade won't pierce the target at all.
So far, this ability was used only once in the series, on Jin, against whom it didn't work. At the end of BlazBlue: Chronophantasma, Tsubaki Yayoi is tasked with utilizing this ability against Rachel Alucard, at the request of Rachel herself, in case that Ragna the Bloodedge isn't slain before his natural death.
Those with the Power of Order, such as Jin Kisaragi and Hakumen, are completely immune to it. The only exception in this case might be Celica A. Mercury, as while she is a manifestation of the Order, she doesn't wield the same type of power as those mentioned above.
The activation code for the Immortal Breaker:
Zero-type restraints released… "Immortal Breaker" activating…
―Tsubaki, BlazBlue: Chronophantasma