Dual! Parallel Trouble Adventures

"Dual! Parallel Trouble Adventure" (Japanese: デュアル! ぱられルンルン物語) is a Japanese science fiction and mecha anime television series created by Masaki Kajishima and produced by AIC, which first aired in 1999. The story follows high school student Kazuki Yotsuga, who is accidentally transported to a parallel world where he becomes the only male capable of piloting the giant robot, "Hartzienen". In this world, he joins Mitsuki, a girl from his original world, to fight against invaders. In the process, he attracts the affections of several women, leading to a comedic harem adventure. The anime combines elements of parallel universes, ancient super civilizations, and giant robot battles. Although many of its settings were not fully explored within its single season, it gained popularity for its lighthearted romantic comedy style. The series is connected to the "Tenchi Muyo!" franchise and is considered to be a prequel, set in the Great Prehistoric Civilization era. It consists of 13 television episodes and one OVA special, and has been released across various platforms, also spawning manga, novels, CDs and other derivative works.