Imaishi began his career at Gainax in 1995 as a key animator on Neon Genesis Evangelion. Some of his early works include animation direction, storyboarding, and key animation in FLCL episode 5, Diebuster, Oval X Over, and the ending animation of Paradise Kiss. Imaishi was also known for his "manga" scenes in Kare Kano (His and Her Circumstances) and FLCL. He went on to direct Dead Leaves, a 2004 anime film produced by animation studio Production I.G., and the first episode of Re: Cutie Honey.