Showa 15 (1940) seems to be the least common of the three. I have kind of a 10 sen coin addiction. Every time I see one in a junk bin I can't help picking one up. I probably have ~200 by now for a grand total of a little over $20. It would be nice to complete a base metal 10 yen date set from Taisho 9 (1920) to Showa 21 (1946). Here's what a random distribution has gotten me so far: Taisho Copper-Nickel: Taisho 9-15 = 1920-26 I have all but Taisho 13, which wasn't minted. (Please ignore that I accidentally put another year 11 where 15 should be. I do have a 15 also.) Showa Copper-Nickel: Showa 2-7 = 1927-1932 I have 2, 3 and 7. 5 Doesn't exist, so I need years 4 and 6, which are quite a bit smaller mintages. Showa 6 is the hardest date of these. Showa Nickel: Showa 8-12 = 1933-1937 I have all but year 8. Year 8 is the smallest mintage by quite a bit, but looks findable. Showa Aluminum-Bronze: Showa 13-15 = 1938-1940 3 for 3! Showa Aluminum: Showa 15-18 = 1940-1943 There was a weight and thickness reduction on Showa 16 from 1.5 to 1.2 g. I think I have both types from that year, so I have the full set. Showa Tin-Zinc: Single year type, Showa 19 = 1944 I have this one. It's plentiful but ugly. Showa Aluminum (post-war type): Showa 20-21 = 1945-1946 I only have Showa 46 (1946) but 1945 is not scarce. There are also several types of red and white porcelain ones from 1945, none of which have I seen in person. I do have a red porcelain 1 sen, but it's cracked. Anyway, if you like 10 sen coins, please post one!