EDIT Late addition This character is a late, »modern« addition to the CJK-languages, a tribute to the influences of the European languages that use the decimal system. It is used very rarely, because in cases where a zero is necessary usually the »pure« decimal system is employed. this is done by use of either the ASCII-characters U+0030 to U+0039 or the Fullwidth-Digits U+FF10 to U+FF19.

 jsw 

EDIT The Chinese numbers 1 to 10 are scattered over various codepoints:

1 一 U+4E00
2 二 U+4E8C
3 三 U+4E09
4 四 U+56DB
5 五 U+4E94
6 六 U+516D
7 七 U+4E03
8 八 U+516B
9 九 U+4E5D
10 十 U+5341

 jsw