When was ~ days ago?

Japanese-era date input is available from January 1 of Meiji 6, when the Gregorian calendar was adopted in Japan.
(Reference)
Meiji runs through July 30 of Meiji 45; that date is also July 30 of Taisho 1.
Taisho runs through December 25 of Taisho 15; that date is also December 25 of Showa 1.
Showa runs through January 7 of Showa 64; Heisei starts the following day, January 8 of Heisei 1.
Heisei runs through April 30 of Heisei 31; Reiwa starts the following day, May 1 of Reiwa 1.

The pop-up calendar is available for dates on or after October 15, 1582, when the Gregorian calendar was adopted.