The LiNKER is a drug originally developed by Ryoko (Finé) as a means to join the power of Relics and the human body. Even with this not just anyone can become a Symphogear user, provided that the subject a certain degree of compatibility, LiNKER can force that rate higher and bring them to the status of acquired candidacy. Of course this process takes a large toll on the human body and it's not uncommon for subjects to receive a shock to their system which results in unconsciousness. Before the drug started producing results it left a lot of dead, or crippled subjects that demonstrated the dangers of the intense medicinal process.
It was for this purpose that LiNKER was further developed with an active time limit and method in which it was cleansed from the body. However these techniques were only obtained by data that Ryoko gained through leaking LiNKER into the black market, and by using it on the test subject Kanade Amou. F.I.S. has a large biochemistry research division that progressed this even further.
Under the charge of Dr. Ver the project proceeded under the theme of "Pleasant for you" and managed to develop a safer form of LiNKER with a very small physical burden and a more thorough cleansing process. Maria, Shirabe and Kirika are all acquired candidates that use LiNKER. Originally they were part of the "Receptor Children" project that was designed to take orphans and use them as vessels for Finé's soul. However one day, Serena demonstrated a remarkably high compatibility rate with the Symphogear and it was hurriedly decided to put all the children through a patch test to isolate those with compatibility.
Thus in the end when the Receptor Children project was scrapped, they were able to become candidates for the Symphogear system instead. In terms of numerical value, the compatibility rate put out by the three is higher than anything Kanade could have obtained, in large thanks to Dr. Ver who has continued to develop LiNKER all this time. They can obtain fighting strength on nearly equal terms to Tsubasa and Chris who are natural candidates.
- After Kanade's death, the LiNKER that she used was kept in the medical room, and was designated as "Model K".
- LiNKER is often injected through the neck, but arm attempts have also happened.