What's the appeal of Half Japanese? This documentary profile by Jeff Feuerzeig makes abundantly and hilariously clear that the punk rock band founded by brothers Jad and David Fair 20 years ago has acquired a rabid cult following. In filmed testimonials, an assortment of fanzine critics and fellow rockers wax apostolic over the band's purity and sweet romanticism, and magician Penn Jillette weighs in with funny anecdotes about how he used money earned from a gig on Miami Vice to fund the label (50 Skadillion Watts of Power) that produced the band's classic album Charmed Life. The commentators also dwell on the perversities of the rock establishment--Rolling Stone, MTV--which they say hasn't given the band its due. By producing this valentine on his own--with earnings from his job directing TV commercials--the 30-year-old Feuerzeig is emulating the Fairs' stubbornly independent spirit. The footage of Jad Fair in performance (including a cover of the Velvet Underground's "I Heard Her Call My Name"), quivering and writhing beatifically, is proof enough of the music's wacky allure. Fair will perform after the Saturday-night screening. Film Center, Art Institute, Columbus Drive at Jackson, Friday, July 29, 8:00; Saturday, July 30, 4:00 and 8:30; and Sunday, July 31, 4:00; 443-3737.