My lover is a housewife, how can I apply for a Japan tourist visa for her?

No need. The premise is that you two apply for a visa together, whether it is an individual visa or multiple visas for three years or five years. If you provide a marriage certificate, you can only provide the assets of the main applicant, that is, you have no assets. The problem is, your wife does not need to provide any assets. The two prerequisites are that first, you two must apply together, not your wife alone, and second, you must have a marriage certificate or a kinship certificate issued by the public security agency. If you have the ability to apply for multiple visas for three or five years, that would be better. Multiple visas allow deputy applicants to enter the country alone.

When applying for the same procedure, only the asset certificate of the main applicant is required