Japan: What are these? Possibly First Day Postmarks?

Picked up some lots I won at the last Rasdale Auction today and found a stamp album with these inside. They look like Japanese First Day Postmarks to me. Has anyone ever seen anything like this?

Manchukuo Covers and Postal History for the year 1944

POSTMARKS and CANCELLATIONS across the globe! [NOT commemorative ones] - #116 by shugal - Mail, stamps & postal info - Postcrossing Community

The Little Mail Carriers in Tokyo!

First Day Covers - Japanese Philately

Update on foreign stamps showing young Americans

First Day Of Issue: Most Up-to-Date Encyclopedia, News & Reviews

The Collector's Series sale - Lots 501-1058 by Spink and Son - Issuu

POSTMARKS and CANCELLATIONS across the globe! [NOT commemorative ones] - Mail, stamps & postal info - Postcrossing Community

How to Ascertain the Date (or Time Period) of Prewar Japanese Picture Postcards – East Asia Image Collection Blog