japan and this isekai have the same problems :
- more women go to work instead of staying at home ,
- low income for men so it is more harder for them to "buy" a wife .
- Japan has the highest proportion of elderly citizens of any country in the world. The country is experiencing a "super-aging" society .
https://knowyourmeme.com/memes/30-year-old-virgin-wizard . i guess the old man is still a virgin , because he is a wizard , lol , so tanker girl is only his adopted daughter .
or maybe he is so senile so he even forgets his previous families , his wives , his children , ....