Japan's current penal code was amended in 2017 for the first time in 110 years to stipulate stricter penalties against sex offenses. But there are still so many loopholes for perpetrators and do little to protect victims, it's appalling. In 2019, a father who constantly raped his daughter from when she was 13 to 19 was found "not guilty," and he was held accountable for only two counts of rape when he was sentenced to 10-years imprisonment in 2020.
In an effort to try and understand how this could be, I researched and was surprised to learn that Japan has never had an all-encompassing, clear-cut law against incest.
There was once a crime called "shinzoku-soukan (incest between relatives)," which was punished under penal codes that were enacted between 1868 and 1873. In some cases, capital punishment was given, until it was abolished in 1880. The catch is, however, that the crime never really included offenses against one's own child*1.
Japanese penal codes are rooted in the laws of the Tang and Ming dynasties and therefore influenced by Confucianism. During the Meiji Period (1868-1912), which marked the end of feudalism and the beginning of "modernization" in Japan, there was a need to create a "Westernized" penal code.
The laws of France and Germany were referred to but incest was no longer considered a crime in France at the time. Drafts by the French legal scholar Gustave Emile Boissonade, which was influential in creating the criminal code, also did not include any provisions regarding incest. Boissonade argued that "authority's intervention in private affairs at home is not appropriate and should be disciplined by morals and religion instead."
Japanese officials agreed that it is better not to include such a disgraceful crime in the penal code—although the crime of having intercourse with a child who is 12 or under has not changed to this day since the Confucianistic Ritsuryo Period. Nonetheless, the crime of intercourse with children by parents was never pronounced*2.
In the feudalistic family system, the head of the house (in most cases the father) had strong authority, whereas women and children were considered to be "properties."
According to Hiroko Goto, the dean of the Chiba University Law School, "it was impossible for the Meiji government to enact a law that restricted the authority of the head, such as incest because it contradicted the mission to promote 'modernization' by giving the head of the house absolute authority."
The crime of "incest between relatives," which existed in an era when the patriarchal family system was even stronger than today, referred to intercourse with fertile women such as concubines, mothers-in-law, sisters of father, wives of descendants, wives of siblings, etc. To rape someone's "property" was not only problematic in moral terms and Confucian ethics but would make it difficult to determine the father of the child, which could lead to confusion in the family line.
That said, the family system could still be maintained even if a father impregnated his own child. In fact, in those times, it was more problematic to not have any children. In other words, it was more important to "protect the family system" than "punish incest with one's own children." To put it in more extreme terms, a sexual relationship between a parent and child was considered "not so bad" in that context*3.
The newly established crimes of "intercourse by a guardian" and "indecency by a guardian" with a child who is 18 or under in the amended penal code of 2017 were long overdue but are still inadequate in protecting children. As in the case of the father-daughter incest case mentioned above, the daughter could not indict him on almost all of the counts aside from the only two when she was 19 because the revised criminal law does not apply to past cases*4.
Moreover, in Japan, the age of consent is set at 13 years old. Under the current criminal law, that means if the victim is 13 or older, the perpetrator is considered not guilty unless it can be proved that there was assault or intimidation to the point where resistance was impossible*5. The age of consent set at under 13 is lower compared to other economically developed countries and the high hurdles of criminal punishment for incest remain for older children.