Zashiki-warashi

Japanese name:

座敷童子

A spirit girl (Vestal sprite) who has a crush on Watanuki.
Zashiki-warashi are prone to mischievous thoughts, though this one is actually quite shy and sweet and very prone to crying (those who make her cry will be attacked by her guardians, a group of tengu-karasu). She lives on a mountain with pure spiritual energy and, as a result, is vulnerable to evil energy.
She is based on a spirit from Japanese folklore, the zashiki-warashi, accounting for her childlike naivety and innocence.

from Wikipedia entry