Book 4: Ghost of the Past is the fourth book in the chapter book series. This book focuses on Ha-Ya-To with his newest battle machine, the Aero Booster.

It was released in June 2007 and was written by Greg Farshtey. It is considered by many to be the best book in the series due to its borderline horror and intense action compared to previous books.


Ha-Ya-To is sent into a strange shaft in the middle of the Golden City by Ryo to retrieve a code, but he is not the only one who wants the codebrick. A few moments after Ha-Ya-To descended into the shaft, a Devastator in a Shadow Crawler follows him.

Ha-Ya-To quickly finds the codebrick and is about to leave when the suddenly a creature swoops down from the rafters, ripping off one of the Aero Booster's massive engines. Ha-Ya-To tries to locate it but is unable to; he plugs himself into a data core that he finds, and stumbles upon a set of journal entires documenting a group of scientists who are working on an experiment. He reads the last entry and finds that the experiment was a success, but not for the scientists; they were forced to leave and close off the shaft so that the creature, nicknamed Nightmare 3, couldn't get out. Suddenly another problem emerges from the darkness; the Shadow Crawler is trapped within the chamber as well. It is about to attack Ha-Ya-To, but it is intercepted by the Nightmare 3 and becomes severely damaged. Ha-Ya-To attempts to bluff that the creature is his friend, but the Robot uses logic to see that Ha-Ya-To is lying.

Ha-Ya-To is forced to do only one thing, accept that the Robot is there, and ask for its help so they can both get out in one peice. The Robot at first declines the offer, stating that it can survive without Ha-Ya-To's help, but it is attacked once again by Nightmare 3 and is badly damaged. The Robot then decides to accept Ha-Ya-To's offer, but only until they both can escape.

Ha-Ya-To and the Robot power down their battle machines and attempt to hook them up together, and they manage to create a bond between the two machines, sharing energy enough to create power for a single blast from the Aero Booster to destroy the creature. Ha-Ya-To pilots an abandoned battle machine that has a slight amount of energy left to get the creature's attention, and it works. They blast the creature, blinding it for a moment, and the two battle machines bolt out.

Once they reach the surface, Ha-Ya-To prepares to fight the robot, but is surprised to hear that the robot does not want to fight. He is even more shocked when the robot says that it will return to its master and report a failure. The human deserves to keep the codebrick, since the Robot could have never escaped without him, and the robot promtly leaves and Ha-Ya-To is left victorious.


  • At the beginning of this book, the author incorrectly calls the Gate Defender the Gate Guardian.
  • Ha-Ya-To gets the Aero Booster before the Golden Guardian in this book, whereas in the comics, he gets the Golden Guardian long before the Aero Booster.


You can listen to Joev14's audiobook version of the book here.

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