The advanced level is doing it anonymously so that there's no paper or digital fingerprint trail that could look suspicious if it came to trial.
The laws around incest and consanguineous (blood related) marriage are really variable. In some places it's perfectly legal to marry an aunt or uncle but incest is illegal in others incest is legal but even cousins can't marry.
(Note that "legal" and "socially accepted" are two very different things.)
In the US incestuous MARRIAGE is illegal. In New Jersey and Rhode Island incest itself (the sex act) is LEGAL. In Ohio it is legal except with "parental figures". It varies by state whether a relationship with a first cousin is incest. In some states incest is narrowly defined. An example is Florida, where incest is sexual intercourse which is defined as a the penetration of the female sex organ by the male sex organ. (Wikipedia link below has a lot of details.)
Only incestuous marriage is illegal in Japan. Two consenting siblings can bang all they want.
Legality of incest in the United States (Wikipedia)
(Note that in the link below some of the countries that are marked as allowing incest in the map it is only allowed for same-sex couples. You can click on a country for "additional details.)
Countries Where Incest Is Legal 2024 (World Population Review)
Incest in the U.S.
In the United States, laws pertaining to incest vary from state to state. All states have laws that make incest illegal but with a wide assortment of exceptions and/or punishments. For example, Rhode Island prohibits incestuous marriages but has no laws against incest in general. New Jersey tolerates incest provided the participants are at least 12 years of age. In other states, including Idaho, Nevada, and Michigan, incest is not only illegal but can also be punished with life in prison.
The legality of incest around the world
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Twenty-two countries around the world have not criminalized incest. Portuguese law, for example, does not criminalize incest. Additionally, no laws prohibit consenting relatives from having sexual relations in France, Belgium, and Luxembourg. Incest is also legal in Argentina, Brazil, India, the Ivory Coast, Japan, Latvia, South Korea, Thailand, and Turkey.