Crane spent half of his childhood in the humiliating care of his overprotective mother Yan Fan, who took extra precautions for his safety by keeping him inside their hazard-free home and putting him in a suit of armor, for she thought her son to be too frail to take care of himself. When he started sneaking out of the house, however, the young crane joined a Kung Fu class that he was amazed by, but it was too advanced for him that he kept getting injured during each session. By the time his mother found out, the sight of what he got himself into gave her heart pains and a hatred of Kung Fu, thus making Crane promise not to practice the martial art again.
Crane eventually grew up still admiring Kung Fu, but kept his distance from it by getting himself the job as janitor at the Lee Da Kung Fu Academy. There, everyone including the strict teacher looked down upon him due to his particularly skinny build and described it as something which made him lack confidence. The class's top student Mei Ling observed the skills which Crane used to tidy up the place every night, and was impressed by his speed and accuracy. She convinced him to try out for the school, and Crane, surprised but encouraged despite it meaning that he would break his mother's rules against Kung Fu, trained himself every night after work until the day of the tryouts arrived.
Kung Fu Panda: Secrets of the Furious Five
Kung Fu Panda Holiday
in Crane on a Wire it is revealed he's allergic to silk