Finished the second disk of Dual! last night, and I like it a lot.
Oddly, neither Geneon nor AIC have any content on their sites regadring the series, but there is a nice little Slovakian fan site with a lot of information about it. The basic plot has to do with high school junior Kazuki Yotsuda, who constantly sees giant robots battling and writes about the battles on his website. Attractive senior Mitsuki Sonoda notics this, and takes him to meet her mad scientist father, who's been dying to find someone to test out his parallel universe transport, mainly to show up his rival Hiroshi Rara. Unfortunately for Kazuki, he's sitting in the wrong place when Mitsuki accidentally activates the tranport, and he soon finds himself in the world where his "imaginary" battling robots are all too real.
Kazuki finds himself in the driver's seat of a robot while trying to save its pilot, and manages to defeat an attacking robot. He then leaves to find some first aid for the wounded pilot, but when he returns, she and the giant robot are gone. The grim reality of the parallel world swiftly closes in: his parents don't recognize him, and neither do his classmates that he encounters on the street. Not knowing what else to do, he wanders back to the deserted Sonoda house - and is taken into custody by a uniformed Mitsuki and a cohort of armed soldiers.
From there on in, Kazuki becomes involved in the war between the UN's Earth Defense Force and Doctor Rara's RaRa Army, a stylized series of conflicts heralded by bombastic previews shown on TV and fought out between the robot pilots of the EDF and those of the RaRa Army. Both types of robots (and the enigmatic bioroid "D", who pilots one of the EDF robots) are the product of alien technology found by this world's Dr. Sonoda (now commanding the EDF and playing father to Mitsuki, Kazuki, and D) and stolen by Dr. Rara. So far it's more comedy than combat, as Mitsuki becomes jealous of D, Yayoi (the pilot Kazuki saved, who becomes attached to him) and frustrated with Kazuki. The scene where Kazuki is fitted with a combat suit intended to disguise him as a girl (since Dr. Sonoda wishes to conceal his male identity) is priceless.