Kazuki is plagued by visions of giant robots that no one else can see. Before Kazuki knows what is happening, he gets ensnared by a pretty face, and then a mad scientist's experiment tosses him into a strange parallel world, where his imagined dangers have become very real!
KAJISHIMA Masaki
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In order to save the world from the side effects of Washuu's latest experiments, Masaki Tenchi goes undercover as a teacher. He is immediately swept up in a conflict between the student council and the science club, who each have a member that is key to Tenchi's mission.
Source: ANN
From Viz:
The trouble and fun began when ordinary teenager Tenchi Masaki inadvertently released the legendary demon Ryoko from his grandfather's shrine. Turned out Ryoko was actually a marooned space pirate! Since then, she's become Tenchi's unwanted houseguest, attracting a host of other troublemaking alien women: Ayeka, a haughty alien pricess; Sasami, her mischievous little…