According to Lotus Sutra Chapter XXV, Avalokitesvara, to save people, manifest herself/himself/itself: #1 into the form of a Buddha, #2 into the form of a pratyekabuddha, #3 into the form of a sravaka, #4 into the form of Brahma, #5 into the form of Sakra, #6 into the form of isvara, #7 into the form of Mahesvara, #8 into the form of the great commander of the devas, #9 into the form of Vaisravana, #10 into the form of a minor king, #11 into the form of a wealthy man, #12 into the form of a householder, #13 into the form of a state official, #14 into the form of a brahman, #15 into the form of a monk, #16 into the form of a nun, #17 into the form of a layman, #18 into the form of a  laywoman, #19 into the form of a wife of a wealthy man, #20 into the form of a wife of a householder, #21 into the form of a wife of a state official, #22 into the form of a wife of a brahman, #23 into the form of a boy, #24 into the form of a girl, #25 into the form of a deva, #26 into the form of naga, #27 into the form of yaksa, #28 into the form of gandharva, #29 into the form of asura, #30 into the form of garuda, #31 into the form of kimnara, #32 into the form of mahoraga, or #33 into the form of Vajrapani. 

     Many of the forms, or manifestations, are an enumeration of occupations at the time of Buddha.  Thus most of the 33 manifestations haven't been carved into Buddhism statues or painted in Buddhism pictures in Japan.  Instead, the number 33 came to mean a lot to Avalokitesvara believers.