ZAIN Terminals are a series of relay computers developed as part of Enterprise's mind-control weapon system, the ZAIN Project. They work within a massive interconnected network spread all over the world which expands the influence of the radio waves used for mind control, released by the "Main Tree" or Yggdrasil. The ZAIN Terminals are extensions of the ZAIN Host Computer and are dependent of it to operate. Conversely, the Host Computer is not reliant on them for functionality, and the project remains operational even if some of the terminals are destroyed.
The terminals appear as towering monstrosities with a strange organic plant-like look, with what appears to be tentacles coming out of their bodies and thousands of cables and wires connecting them with computer terminals surrounding them. They don't appear to have a mind of their own, thought they do emit a rare screeching sound as if they were living beings.
During the course of 30 years, steady research and development of the ZAIN Project led to the creation of the ZAIN Terminals. It is said there are several units spread across the world, with three specific locations mentioned: two fully operational terminals located in Kazakh and the Amazon, plus a third one mentioned to exist in the Sahara desert.
The majority of the project's development was carried in the ZAIN lab hidden within the Kazakh Federation Mental Institute, overseen by its director. Through an association with the corrupt secret police of Kazakh, the institute held a supply of human guinea pigs for experimentation. The research's work was later tested with the brainwashing of Hiryu's sister and A Rank Strider, Mariya, although her becoming violent afterwards proved to be a failure of the process.
Two years afterward Kain is subjected to the same experiments, with similar results. This act, however, leads into Hiryu's involvement and discovery of the project. Seeking revenge for the deceased Sheena and his manipulated sister, Hiryu brings down the whole institute and the terminal with it. Later, they infiltrate and destroy the ZAIN Terminal found in the Amazon Institute, but not before tracking down the Host Computer's location through its satellite link.
There are 4 ZAIN Terminals developed by The Syndicate: two in Africa, one in Kazakh and one in China. After Kain fell captive of Kazakh's police during his investigation, he was subjected to the brainwashing as well.
Once Hiryu rescues him, he discovers through Kain about the mysterious project, and following Kain's suggestion, visits Chief Kuramoto in Japan. The Chief reveals to Hiryu the true nature of the project, and sends him to destroy the Chinese terminal. Before being able to do so, however, he has to knock out a brainwashed Kain. With the revelation that his sister suffered similar symptons and was likely another victim of the project, Hiryu swears to put an end to the project.
The ZAIN Terminals are stationary bosses, remaining still in the background. They have a defense system in the form of a square machine that travels throughout the borders of the screen, raining down a set of four orbs when at a specific location, usually high above Hiryu. These defense machines can also damage through contact, but are otherwise very easy to avoid and destroy.
Once the defense machine is taken out, the ZAIN Terminal starts to attack by throwing out bombs at Hiryu's general direction, which explode once they hit the ground. The terminal's weak point is found in its "head" or core at the top of the machine, so one needs to jump while avoiding the bombs and strike there to destroy it.