And with that I have to ask: What about it makes it kids programming at that point? The presentation? The idea that heros simply appeal more to children than adults?
When you're dealing with Japanese media, there's two key factors to look at for determining intended audience: ratings demographics, and timeslot. Based on a look at those two factors, Garo is absolutely a show for adults, and Heisei Kamen Rider absolutely is not.
Heisei Kamen Rider episodes air at 8 AM on Sunday mornings, as part of the Asa Nichi Kids Time Block. It airs sandwiched between Toei's Super Sentai franchise, and Toei's Pretty Cure franchise. Both franchises target extremely young children, think about 3-6. Super Sentai skews more towards boys, and Pretty Cure more toward girls. If KR was really aimed at adults to any significant degree, it would make no sense to schedule the program this way.
That said, Kamen Rider is generally the cornerstone of the Asa Nichi Kids' Time block, and draws the highest ratings. So could you argue that it's the most popular program because it draws the broadest audience, due to its adult appeal? Perhaps, but if you look at ratings demographics, most shows simply don't draw a significant number of viewers older than 12. This was true even back during Heisei Rider's "dark" era, when shows like Faiz and Blade were the franchise's standard bearers.
As proof, here's a comparison of the demographic ratings data for every Heisei Rider series where it's available. This generally starts with Faiz and goes up through Fourze (Wizard's probably won't be out until next year). Japan reports ratings by population, so the ratings numbers represent what percentage of the Japanese population tuned in to a specific program. The demographic ratings work the same way, showing what percentage of Japanese persons in a given age range opted to watch the show. The numbers I'm choosing to compare are the general (total population) rating, the kids rating (viewers under 12), the teens rating (viewers 13 to 19), and the M1 rating (male viewers aged 20 to 35). I'll be comparing figures from the first episodes of the various series, since that's generally when Rider viewership is highest.
Faiz Episode 1:
General: 10.5%
Kids: 23.4%
Teens: 5%
M1: 3.9%
Blade Episode 1:
General: 10%
Kids: 16.4%
Teens: 2.5%
M1: 4.4%
Hibiki Episode 1:
General: 8.6%
Kids: 13.6%
Teens: 1.1%
M1: 4.3%
Kabuto Episode 1:
General: 10.9%
Kids: 17.3%
Teens: 2.8%
M1: 5.8%
Den-O Episode 1:
General: 8.5%
Kids: 12.8%
Teens: 4.9%
M1: 4.6%
Kiva Episode 1:
General: 7.6%
Kids: 11.6%
Teens: 2.1%
M1: 3.6%
Decade Episode 1:
General: 6.3%
Kids: 9%
Teens: 0.2%
M1: 4.2%
Double Episode 1:
General: 10.2%
Kids: 15.2%
Teens: 4.2%
M1: 10.3%
OOO Episode 1:
General: 10%
Kids: 15.4%
Teens: 6.3%
M1: 6.6%
Fourze Episode 1:
General: 6.3%
Kids: 10%
Teens: 2%
M1: 3%
By now it should be clear that no demographic likes Kamen Rider better than children under 12. Kamen Rider simply wouldn't sustainable if it targeted other demographics, due to lack of viewership (though, Double might be able to get by doing that). I don't think this would be the case so consistently if Kamen Rider was "really" a property for the 14-30 crowd that just happened to be marketed aggressively to children. I would say Kamen Rider is more like, say, Nickelodeon's Airbender shows, a property that lives or dies on kid appeal, but also happens to have an older fandom that appreciates the property's more sophisticated elements. Generally, good children's entertainment will be something an adult can enjoy to some degree.
Now, let's look at Garo. Its original timeslot information is lost, but it is generally known that it aired after midnight. Its sequel, Makai Senki, aired from 1:45 AM to 2:15 AM. It's unthinkable that many kids would even be up regularly at that time, let alone watching TV. Plenty of folks over 18 end up with reasons to burn the midnight oil, though (or experience simple insomnia). Generally post-midnight shows in Japan tend to be products aimed at older-yet-geeky audiences, and can include more sexuality, violence, and dark themes than their prime time or morning counterparts. Demographic data for Garo viewership isn't available, but generally the ratings ranged from 0.5 to 1.5% (as befits a post-midnight time slot).
So how did the show survive, let alone spawn a sequel? Again, this points at its intended audience. Garo was overwhelmingly aimed directly at older fans, who generally have more disposable income than younger folks. These viewers are far more likely to support a show by purchasing it on home video, or buying lots of pricey collector merchandise like figures and replicas. By aiming at a small but cash-heavy demographic, it's possible for Garo to turn a profit despite being made on a much smaller budget than Rider, and generally being seen by fewer people. In this way, Garo is fundamentally unlike Rider, despite probably being targeted at the sort of grown-up who also chooses to keep up with Heisei Kamen Rider.
Toku is a big enough genre, just like american comics, that some of it can be called kids stuff and others can't.
You are totally right here. That said, I think Rider is just not in the segment of tokusatsu that
can't be called kid's stuff. Yuusha Yoshihiko, Cutey Honey the Live, Shibuya 15, Youkai Ningen Bem, the Magister Negi Magi tokusatsu, the Ranma 1/2 tokusatsu, the Arakawa Under the Bridge tokusatsu... yeah, definitely not for kids. Everything about these shows screams "not for kids," from scheduling to marketing to content. Rider is pretty much for kids, though, even if it touches on more mature themes from time to time.
