Japanese numbers:

Pre-1867 coins require more expert help than is given here.

List of emperors from 1867:
Mutsuhito (Meiji), 1867-1912, years 1-45
Yoshihito (Taisho), 1912-1926, years 1-15
Hirohito (Showa), 1926-1989, years 1-64
Akihito (Heisei), 1989- , years 1-

Japanese coins are dated by ruling emperor (year of accession) plus the regnal year.
Prior to 1948 regnal numbers are read from right to left.

Examples:

Emperor (Mutsuhito) regnal year from R to L = 2 x 10 + 6.
Date 1867 + 26 = 1893 AD.

Emperor (Yoshihito) regnal year from R to L = 10 + 1.
Date 1912 + 11 = 1923 AD.

After 1948 (reform coinage) regnal numbers are read left to right.

Emperor (Hirohito) regnal year (now L to R) = 5 x 10 + 6 = 56.
Date 1926 + 56 = 1982 AD.

Since the 1960s fifty yen and higher denomination coins use western numbers for the regnal year.

Emperor (Hirohito). Year = 1926 + 42 = 1968 AD.

The symbol denotes the 1^st year of the reign.

Emperor (Akihito) 1^st year of reign = 1989 AD.

Emperor (Akihito) regnal year = 10 + 7. Year = 1989 + 17 = 2006 AD.