And people are trying to figure out why.
One debated factor is the rise of sōshoku-kei danshi, or "herbivore men," a term coined in 2006 by columnist Maki Fukasawa.
"In Japan, sex is translated as 'relationship in flesh,'" she told CNN in 2009, "so I named those boys 'herbivorous boys' since they are not interested in flesh."
Herbivores are increasingly present in Japan, according to a 2015 survey of 1,134 people 16 to 49, as reported on in The Japan Times.
"Among male respondents, 17.9 percent reported little or no interest in having sex — or even an extreme dislike of it," The Japan Times reports. "The proportion came to 20.3 percent for men between 25 and 29, up 2.5-fold from the level in 2008."
At a macro level, it's understandably troubling. When 48% of men and 50% of women report not having had sex in the past month, it's not going to help the "demographic time bomb" that's coming toward the country.
The lack of ardor may be related to the fact that, like many societies, Japan struggles with mental health.
It's notoriously hard to measure. A 2013 study showed that Japan has the lowest clinical-depression diagnosis rate in the world, though some critics think that's because of a lack of recognition of the "clinical" aspect of depression.
The country's notoriously long work hours — think 80-hour weeks — appear to also have an effect on sexuality. Over 20% of the married men in the Japan Times study said they weren't interested in sex because they were too tired from work.
But on the other hand, the "herbivorization" may also represent a revolution of identity politics in the island country.
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Herbivore men "have some feelings of revulsion towards the older generation," Fukasawa said in another interview. "They don't want to have the same lives. And the impact of the herbivores on the economy is very big. They're such big news now because sales are down, especially of status products like cars and alcohol."
And as with all good buzzwords, the "herbivore" terminology has given rise to an entire range of heterosexual identifications.
Japan Times blogger Rebecca Milner supplies a taxonomy:
- nikushoku-kei danshi (肉食系男子; carnivore guys): Classic macho guys who go after what and who they want.
- sōshoku-kei danshi (草食系男子; herbivore guys): Shy guys who don't make a move. They are prey for the growing number of nikushoku-kei josei (carnivore girls).
- roru kyabetsu danshi (ロールキャベツ男子; roll-cabbage guys): Guys who appear to be herbivores but are actually carnivore to the core. They are named for the classic yōshoku — Japanese-style western food — dish of cooked cabbage stuffed with meat.
- asupara bēkon-maki danshi (アスパラベーコン巻き男子; bacon-wrapped asparagus guys): Guys who come across as carnivores but later reveal themselves to be herbivores. Named for the yakitori dish.
- zasshoku-kei danshi (雑食系男子; omnivorous guys): Guys who will go with whatever works.
- zesshoku-kei danshi (絶食系男子; fasting guys): Guys with zero interest in women.
But here's the thing: While this may be imprinting Western ideals on Japanese culture, it does seem that all these herbivores serve a long-term good.
If we hold that people should be able to express their sexual orientation in the ways that they identify as — opposite-sex or same-sex, sexual or asexual — then the rise of the herbivores is progress, a liberalization from the strictness of hypermasculine "salarymen" that have been conferred alpha status in Japan since World War II.
Identity progress is slow going in Japan. It's a country that is just beginning to have a national LGBTQ conversation, and it went into a racist tizzy about Miss Universe Japan 2015, who is biracial.
So while "herbivorization" might be a problem for getting the birthrate up, it's the start of an answer as far as gender and sexuality are concerned.