LCL is an amber-colored, translucent liquid, which allows an Eva pilot to mentally link with their Evangelion Unit. The Entry Plug of an Eva Unit, containing its cockpit, is completely flooded with LCL, and, because it is oxygenated, upon being submerged Eva pilots can "breathe" the liquid (similar to real-life experiments involving
Upon Evangelion activation, an electrical current is run through the LCL and it undergoes a "phase shift", after which its density, opacity, and viscosity appear to approach that of air. However, the LCL remains in a liquid phase and does not undergo a transition: the pilots appear to be surrounded by air, however occasionally air bubbles will float away from their mouths, revealing that they are still in a liquid medium.
When an Eva activates, the pilot is totally submerged in LCL in the entry plug. The LCL acts as a mediator allowing the pilot's nervous system to electro-chemically directly interface with the nervous system of an Eva. The greater the degree of interfacing between an Eva and its pilot's minds, the higher the "synch ratio" between the two.
LCL is strictly the only thing a pilot absolutely requires to sync with an Eva: plug suits "cut down on interference" but on several occasions, the pilot hasn't worn one, and while Interface Headsets are much more necessary to sync, when Shinji piloted Unit-01 for the final time in The End of Evangelion he did not wear an Interface Headset (although by that time he was essentially a passenger inside the Eva). Case in point, Toji and Kensuke, wearing neither plug suits nor interface headsets, manage to induce interference in Episode 03 when they enter the entry plug.
It is stated several times in the series that LCL smells "like blood". LCL is, in fact, the blood of the Second Angel, Lilith, which is restrained in the deepest level of NERV HQ, "Terminal Dogma". The "LCL Plant" in Terminal Dogma is actually an entire lake formed from the blood of Lilith.
LCL shares similar properties with the hypothetical "primordial ooze" from which life on Earth first evolved. This is because non-Angel life on Earth actually originally evolved from the LCL spread by Lilith when she landed on Earth. During Third Impact, Lilith's Anti A.T. Field causes the A.T. Fields of human beings and all other Lilith-based life to collapse, reverting their bodies to puddles of LCL.
An amber-colored fluid, visually identical to LCL, escapes from Leliel's body (the ultra-flat "shadow") when the bullets of Unit-01's handgun strike in Episode 16.
- In the Rebuild of Evangelion continuity, LCL is colored blood red, not orange.
- The real-world version of LCL as a breathable liquid is a class of chemicals called or PFCs. At least 5 different PFCs are in different stages of testing for liquid breathing: , , , , and , with perflubron and perfluorohexane both having been tested successfully on humans (perflubron used to help prematurely born infants breathe, and perfluorohexane used to help burn victims breathe). PFCs, most notably perfluorodecalin, are also used as blood substitutes to deliver oxygen to the cells of people who have lost blood if a blood transfusion is not available. Notable differences they have from LCL are they are clear instead of orange or red, they are twice as dense as water instead of less dense, they do not become ionized, and even if they were part of the primordial soup of life they were just a minor part of it.
- The real-world version of LCL as the "primordial ooze" is the that was first briefly mentioned as a "warm little pond" by Charles Darwin in his book On the Origin of Species in 1859, developed into a complete theory for the origins of life in 1924 by Alexander Oparin, and then duplicated in a lab in 1953 in the . In that experiment, 4 simple chemicals (water, methane, ammonia, and hydrogen) were used to create a variety of amino acids. Those amino acids are the building blocks for proteins and for all life on Earth, even more fundamental to life than DNA or RNA (in fact DNA and RNA are simply codes for which amino acids to assemble in what order to construct proteins). Subsequent similar experiments have produced a wider array of chemical building blocks of life including the nucleotides from which DNA and RNA are composed, confirming these results.
- Due to its orange color, LCL is often referred to as , an orange juice drink, by fans. Instead of saying, "reverting to LCL," fans will often say, that a "(character) was Tanged", calling the process "Tangification", etc. The color of LCL was changed to blood red instead of orange for Rebuild of Evangelion, thus ending the similarity to Tang.
- LCL is definitely an abbreviation for something: other words in the series spelled using all-capital letters such as "NERV", "Gehirn", and "SEELE" are not acronyms, but instead were simply spelled using all-capitals as a quirk of translation. "LCL", however, is confirmed to be an abbreviation because it is sometimes seen spelled as "L.C.L." on computer displays, though simply "LCL" is much more common.
- It is unknown what the initials "LCL" stand for, but we do know what they don't mean. According to the Evangelion: Death and Rebirth theatrical program (special edition):
- "Incidentally, the widely circulated idea that L.C.L is the abbreviation of "Link Connected Liquid" is incorrect."
- However, nowhere does it say what it does mean. Why they would go out of their way to say what it doesn't stand for, but not go on to explain what it does stand for, is unknown, and a cause of much fan frustration. Evangelion Chronicle suggests that one of the Ls stands for "Lilith".
- In a dossier at the end of Volume 7 of the manga, it is claimed that L.C.L. stands for "Link Connect Liquid", contradicting the previous statement.
- The Spanish word for "sky" or "heaven" is "El Cielo". The Sea of LCL in The End of Evangelion seems to be in space. If this similarity is deliberate and not a coincidence, it makes LCL a wordplay on "heaven".
- Looking at the similarities and references of LCL to the hypothetical primordial soup of life, a possible meaning to the acronym LCL could very well be "Life Component Liquid", or a derivative thereof.
- The Qabbalah, an important part of Jewish mysticism, equates the blood with the lowest aspect of a human soul called nepesh (נפש). See Leviticus (ויקרא) xvii:xi and Deuteronomy (דברים) xii:xxiii.
- The LCL fluid inside of the Entry Plug is oxygenated, thus when Ramiel's energy beam strikes Eva Unit-01 in Episodes 5 and 6 and Shinji is being "boiled alive", you can see that the heat is causing all of the oxygen to bubble out of solution.