Berserk
Berserk (暴走, bousou) is a state an Evangelion can enter into in which she has gone beyond Nerv's ability to control her, entering into a savage battle-frenzy in which the Eva's strength and ability levels drastically increase. In most cases, a berserk Evangelion can, inexplicably, continue to function even after her internal batteries have been drained, i.e., remain operational beyond the established time limit. Characteristically, during "berserker mode" those Evas with jaws bolted shut will violently force them open and bellow wildly, and show other animalistic tendencies in their movement
During these incidents, the Eva's resident soul appears to bypass restraint mechanisms and wield her own body, although it is arguable how much conscious control the soul has over the Eva's actions. (The discrepancy between the behavior of Yui Ikari — prior to her "death" — and her Evangelion incarnation is often cited to this effect.)
"Berserker mode" operates in defiance of the current level of human scientific knowledge, and as Dr. Ritsuko Akagi says of the Angels in Episode 04, Nerv is truly dealing with beings beyond the grasp of modern science's comprehension. Ritsuko is aghast when Eva-01 goes berserk in Episode 16 with its internal batteries completely drained, and in Episode 20 it is revealed that no known power source could be detected during the incidents when the batteries were drained. No attempts at artificially initiating berserker mode were attempted by Nerv, quite possibly due to the extreme risk of an uncontrollable, overpowered Eva. Nor, even at the utmost need, can an Eva pilot voluntarily initiate berserker mode (with one exception, see below): it's simply something that happens when, and only when, the soul contained inside the Eva feels that the need is great enough to warrant it.
A pilot completely loses any control whatsoever over an Eva when she has entered berserker mode, and is really just a passenger at that point, while the Eva's resident soul takes control. It doesn't even seem that an Eva pilot is conscious anymore when an Eva goes berserk: when Eva-01 goes berserk in the battles against Sachiel, Leliel, and Zeruel, in each instance Shinji appears to have blacked out when berserker mode initiates. Thus, not only does berserker mode not reflect a pilot's voluntary decisions, a berserk Eva's actions are also in no way influenced by a pilot's own subconscious mind (i.e. Eva-01 is absolutely not "acting out Shinji's subconscious desires" when she goes berserk). The exception to this is during Asuka's final battle with Eva-02 (explained below).
The fullest extent of berserker mode is when an Eva loses control and continues to function, even after its umbilical power cord is severed and its internal power limit has been exceeded. Sometimes an Eva can go berserk and the umbilical cord is still attached to the Eva (i.e. Eva-01 in the battle against Sachiel), although it may not be necessary at that point. Eva-01 also once moved without power, and also without entering a combat frenzy (to shield Shinji from falling debris, see below), but this is the only instance of an Eva not running amok when it enters berserker mode.
Eva-00 has two incidents (in Episode 05 and Episode 14), both occuring when a pilot attempts to synchronize with her for the first time. During her activation test with Rei Ayanami, the Entry Plug is auto-ejected (apparently by the Eva herself) and Eva-00 continues to move undeterred until her power runs out. The second incident, involving Shinji Ikari, is extremely similar, except the Eva rejects the auto-eject signal. This prompts a cryptic comment from Ritsuko, "Is it going to try to absorb Shinji?" It is not clear, however, due to these circumstances if the two incidents of Eva-00 losing control should strictly speaking be considered true berserker mode, and not simply "losing control". Case in point, Eva-00 turned off after her normal internal power supply ran out, which an Eva in true berserker mode would have been able to keep functioning beyond.
Eva-01 is the most notorious "berserker". Her abilities to move both independently of a pilot and without power are effectively established before her initial activation, when she moves her arm to shield Shinji from falling lights (in spite of being loaded with a Termination Signal Plug). Not long after, she goes out of control during her first sortie, against Sachiel, exhibiting a bestial and uncompromising battle rage that doesn't stop until the Angel is down. Similar behavior occurs when Eva-01 brings about Leliel's gruesome destruction, and, later, mauls and devours Zeruel, although, unlike the incident with Sachiel, these both occur when her internal batteries are fully drained. In The End of Evangelion, Eva-01 moves independently once more, freeing herself from restraint in bakelite so Shinji could pilot her, then setting off a crucifix-explosion and growing wings of light. From this point forward, Eva-01 seems to be in complete control of herself.
Eva-02 sets off a crucifix explosion and goes into a battle rage in Episode 25', performing incredible acrobatic feats and casting an offensive A.T. Field against attacking JSSDF units. After losing all battery power and being ravaged by the Mass Production Evas the Eva goes berserk (for the first and only time) and moves without any power supply, moments before its destruction. This instance of going berserk is unique because it is the only instance of the pilot synching with the Eva during berserker mode: in contrast, Shinji appears to take no part at all in Eva-01's control when it goes berserk. It is possible that this is because, as Asuka herself proclaimed, she by that point had fully realized that her mother's soul was inside of Eva-02, "watching over" her, and was thus able to integrate her actions with those of her mother's soul; Asuka's synch ratio did appear to be higher than it had ever been judging from the skill she displayed in the battle, and the sympathetic physical damage she sustained at the end. Shinji, by comparison, did not fully comprehend that his mother's soul was contained in Eva-01 during the battles against Leliel and Zeruel, etc.
Eva-03 was infected by the Angel Bardiel during activation and initially behaved very much like Eva-01 in her first berserk incident, breaking open its jaws and bellowing, although this appears to have been the work of the Angel and not the resident soul. Despite being heavily mutated by the Angel, Eva-03 was ripped apart by a Dummy Plug controlled Eva-01, so the Angel appears to have been unable to harness the latent power and strength of a truly berserk Eva.
Notes
- Bousou literally means "out of control". "Berserk(er)", however, is the official English rendition, as indicated by the document Shiro Tokita displays in Episode 07.
- When controlled by the Dummy Plug system in Episode 18, Eva-01's behavior is indistinguishable from her true "berserker mode".
