Parallel Dual! Ultimate Fan Guide (2002)

This is another fan guide/RPG setting book from Guardians of Order.

This book is slimmer than most of their RPG/fan guides, and requires the main Big Eyes. Small Mouth 2nd Edition book if you want to use the game information to run a game.

From the introduction:

Dual! chronicles the adventures of a 16 year old high school student, Kazuki Yotsuga, who finds himself transported to a parallel Japan. In his home world, Kazuki's classmates mock him for the visions of giant battling robots only he sees. In the parallel world, he discovers that these robots are real and are fighting a war for world domination, using his home city for a battleground. He also learns that he is the only male in the parallel world who can pilot the giant mecha, which makes him an important asset to both sides - and places him in great danger.

The artwork all appears to be shots from the series, or the character model designs.