Properly called the ZAIN Host Computer, Yggdrasil is the core system of the ZAIN Project, developed as a mind-control weapon. It is the center of a larger network of smaller ZAIN Terminals spread all over the world to help expand its influence worldwide. It's stated it is powerful enough to process 50 billion transactions at once, with expectations to rise its processing power to one hundred billion data after an upgrade. The ZAIN computer can be also used to predict specific scenarios: it determined with a possibility of 96% that Hiryu and Kain would target the Amazon Research Institute following their destruction of the Kazakh Federation Mental Institute.
The ZAIN Host Computer is the central core computer controlling Enterprise's ZAIN Project. A massive computer terminal, it has been build as part of the large skyscraper that serves as headquarters for Enterprise. The machine's core is located at the underground floor of the building, in a room covered by several connection cables surrounding it. In the terminal's front stands a throne used by Faceas Clay. The whole room is under protection of a specially-designed defense system exclusively, due to Clay's distrusts of humans.
Yggdrasil is the product of 30 years of intensive research over brainwashing control and testing on human guinea pigs provided by Kazakh's Secret Police. The project has remained a highly-classified secret, since Faceas Clay plans on using it to control all humanity. Although it appears to be simply a computer terminal, it is slowly developing a mind of its own.
Hiryu reaches the top floor of the building and confronts Faceas Clay, successfully defeating the defense system and killing the cold-hearted man. Hiryu is later confronted by Matic until the appearance of a large group of Striders. After Matic is cornered by his former subordinates following Kuramoto's exposition of his betrayal, he attempts to threaten them with a bomb. However, just then the Mother ZAIN releases one of its cables and pierces through Matic, killing him instantly. Yggdrasil starts talking about its directive is to protect the "foolish humans" and to lash out against anyone standing in its path, using its many appendages to attack all Striders present. Hiryu gathers his remaining strength and throws his Cypher at its core, destroying the machine and ending the ZAIN nightmare for good.
Yggdrasil is the central vital core of the ZAIN Project. The Syndicate created this massive computer system after years of research and experimentation. Yggdrasil can control the brainwashing aspect of the project, but requires support of smaller "child" terminals in order to increase its effective range.
When Hiryu infiltrates Matic's Red Dragon base, he's already aware of the existence of the Yggdrasil from a previous fight. Yggdrasil rests in the heart of the station, under protection of its own defense system as well as Matic's subordinates. Hiryu, however, battles his way through the opposition, defeats Matic and finally destroys Yggdrasil, putting an end to the ZAIN Project.
Yggdrasil is a stationary boss much like the ZAIN Terminals, but lacks the square machine that serves as a defense for the latter. As soon as Hiryu enters the chamber, Yggdrasil releases two disc-shaped projectiles from its core, which cross paths in the middle and then fly away, staying close to the edges of the screen. As this attack is going, Yggdrasil throws two bombs at Hiryu's direction, identical to the ones used by the generic Terminals. After the discs leave the screen, Yggdrasil releases a new set and repeats the pattern.
Much like the ZAIN Terminals, Yggdrasil's weak point is found on its core or "head", so destroying it is simple a matter of dodging the many projectiles while striking at the core. The most effective way to fight Yggdrasil is to use the Cypher's "Up" strike while jumping straight up at the core.
- "Yggdrasil" is named after the sacred World Tree of Norse mythology. In the manga, this name is only used by Faceas Clay, as an analogy about it being the start of a new world, much like the mythological one.
- In the original manga, the ZAIN host computer looks greatly different in appearance from the game's Yggdrasil, but both share the same basic function in the story.
- The manga grants a few different and interesting names to it: Hiryu refers to it as "Mother ZAIN" (ザインの母体(マザー)), while Faceas Clay calls it Yggdrasil/"World Tree" (世界樹(イグドラシル)). Hiryu and his allies also refer to it derisively as a Devil's Weapon (惡魔の兵器), and since it is the core of the ZAIN Project, it is also referred to as the "Main Tree".
- Wada, Tatsumi (November 10, 1989). Strider Hiryû. Chapter 3, Pg. 114. Kadokawa Shoten. ISBN 4-04-713009-5.
- Wada, Tatsumi (November 10, 1989). Strider Hiryû. Chapter 5, Pg. 162. Kadokawa Shoten. ISBN 4-04-713009-5.
- Wada, Tatsumi (November 10, 1989). Strider Hiryû. Chapter 4, Pg. 122. Kadokawa Shoten. ISBN 4-04-713009-5.
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- Capcom (July 1989, NES). Strider (English). Scene 10: Yugdesiral