Mai

A student at the Santa Claus Academy that has problems using her magic. She can only conjure up things that start with "san" (サン) in the Japanese language. She was sent to Santa to cheer him up as her mission. Mai first appears to Santa as a junior high school student. Later when Santa starts to believe in Santa Claus, Mai gains enough Christmas powers to change into her grown up form. In adult form, Mai oddly uses the hyper-masculine "ore" (as opposed to the traditionally feminine "atashi") when referring to herself, despite the feminine appeal that she gains with her transformation.

[Wikipedia]