Japan reformed their coinage after the World War starting in 1948 AD, corresponding to the 23rd year of the Showa era. With the reform, a new metal and a new design was introduced. The bird within the obverse circle is supposedly a pigeon - looks more like a chicken to me! Halfway through 1949 (Showa 24) Japan introduced a center hole to their 5 yen coins, and the design was changed again. No birds or buildings on the later coins, just a rice plant and some small sprigs for decoration. By the way, the center hole saves a whopping quarter of a gram per coin, which allowed the Japanese mint to strike 17 holed coins for every 16 non-holed coins. What a saving!
Typical average values for the coins without holes are:
COINS DATED 1948 (Showa 23):
average circulated: less than $1
well preserved: $1
fully uncirculated: $12
COINS DATED 1949 (Showa 24):
well preserved: less than $1
fully uncirculated: $8
As can be gleaned, coins dated 1949 are extremely common (almost 200 million were made!) and there is almost no demand for coins with any trace of wear. The 1948 date is better only in the sense that 'just' 75 million were made, which is still a great number. Only coins with great eye appeal are in demand, though with this date collectors may look past a small degree of wear as long as the coin is still very attractive.
Any coin with severe damage is worth essentially zero. Remember that the catalog values cited above are not equal to actual buying and selling values. See our Important Terminology page at the top left for more information.