Modern Japanese urban environment is an evolutionary mismatch for the human animal.
The solution to falling birthdates isn’t immigration. It’s cultural.
Encourage natural human interaction, sex, physical fitness and spirituality:
* ban Tenga fleshlights and “Japan Real Hole” custom pornstar pocket pussies being sold in Don Quixote grocery stores
* replace conveyor belt sushi and restaurant vending machine ordering, with actual human interaction with a waiter
* replace 24/7 eSports cafes where young males earn false fitness signals via Tekken fighting and Overwatch shooting games, with athletics in school
* heavily stigmatize maid cafes where lonely salarymen pay young girls to dress as anime characters and perform anime dances for them
* revitalize traditional Japanese culture (Shintoism, Okinawan karate, onsen, etc)