get a 5 year marriage visa, divorce immediately, you good for 5 years

Nooo... It doesn't work like that. Unless you have PR, your visa is tied to the performance of certain activities. (Spouse = maintaining a real marriage; Work = engaging in or seeking to engage in the relevant types of employment; Student = studying.) Residing in Japan for 90 days without performing those activities (e.g. by being divorced while on a spouse visa) is grounds for revocation of your visa, regardless of what's written on your residence card.

Also, you must report all changes that affect your visa-designated activities, like getting divorced while on a spouse visa, losing your job while on a work visa, or graduating/quitting while on a student visa, to Immigration within 14 days.