When Armisael first attacked Eva-00 and its pilot, it made Rei experience real emotions for the first time. It made her realize that she was truly lonely in her existence and had never opened herself to anybody, not even those closest to her. Then Shinji appeared in Eva-01. The sixteenth Angel tried to attack him too, but Rei held it back and self-destructed her Eva in an attempt to destroy the Angel before it could hurt Shinji.
Profile: Armisael was a shape-shifting Angel that originally had the form of a double helix (like the Lance of Longinus) closed up in a circle. Its main means of attack was to merge with the Evas and attack the minds of the pilots.
Fate: Armisael was vaporized in the blast (as was most of Tokyo-3) caused by Eva-00's self-destruction.
Notes: Rei II was killed in action. Armisael is the patron Angel of the Womb.