is a Japanese anime series animated by AIC and created by Masaki Kajishima, best known for the Tenchi Muyo! franchise. It was originally broadcast on Wowow from April to July 1999 and was licensed in the US by Pioneer LDC, later known as Geneon. In addition to the original TV run, an OVA special was added to conclude the series as a de facto "14th episode". The title refers to the fact that the story takes place in two parallel universes, a concept loosely based on multiverse theory. Plot 22 years ago, a huge alien artifact is found on a construction site by a worker named Yotsuga. The foreman orders that the artifact be broken apart to avoid delays. As Yotsuga walks towards the dumpsters to dispose of a small piece of the artifact, the world splits into two. In one world, Yotsuga tosses away the piece and the artifact is destroyed. In the other world, Yotsuga keeps the artifact, leading to the discovery of extraterrestrial technology that changes history. In the present, Kazuki Yotsuga is a high school student who is shunned by other students as an otaku; his web site describes battles between giant robots that only he can see, but it is mostly as a result of him being occasionally seen by the other students reacting to their "presence". One day, the most popular girl in school, Mitsuki Sanada, approaches him to tell him that she likes his stories. This is only a ruse; she lures him to her father, Dr. Ken Sanada, who wishes to study Kazuki for his research on parallel worlds. After being thrown into the other possible world by Dr. Sanada's device (thanks to a careless action by Mitsuki), Kazuki finds himself still in Dr. Sanada's basement, but everything is covered with cobwebs. Kazuki goes home, is distracted by a real battle between two giant robots, one white and the other black. The white robot is knocked down and an injured female figure emerges from inside. When Kazuki goes to her aid, he is trapped inside the robot and somehow manages to activate it and defeat the enemy robot. Afterwards, Kazuki reaches his home, but his parents no longer recognize him. He is found by Mitsuki, who has followed him. Along with a military escort, she takes him to the Earth Defense Force HQ, a paramilitary operation led by this world's Dr. Sanada.