Help Identifying A Japanese 1 Yen Aluminum Coin

Can anyone help identify this possible Japanese 1 yen mint error?
I found what appears to be a Japanese 1 yen aluminum coin.
Weight: 1.00 gram
Plain edge
Aluminum (very light)
High-pitched ring when tapped
Design matches a genuine Japanese 1 yen coin.
The unusual part is that there appears to be no date where the date should normally be between the characters #19968; and #20870; on the side with the tree. I don't see any evidence that the date was ground or polished off, and the surface feels the same as the rest of the coin.
I'm wondering:
Is this a known Japanese mint error (such as a struck-through grease error or missing-date error)?
Or is it more likely a token, replica, or altered coin?
I've attached photos of both sides, the edge, and close-ups of the date area.
Any opinions from collectors familiar with Japanese coins would be greatly appreciated!