These guys love history, and historic stuff.  Many older people fall into this category, but also certain types of people or professions (like architects, etc.) are common.  These people love Japan for its long history, which I can't blame them for.  Japan doesn't exactly have the longest recorded history, and loses out to countries like China - but especially compared to the US, it has a flavor all its own.  Liking historic Japanese buildings is one thing.  Assuming that normal people still live (or want to live) in them is another.  Tatami are still used, but now they are used for "Japanese style" (old style) rooms in 60 story glass and steel sky-scrapers.  People also still wear kimonos, but only for special occasions, or if they work at a tourist shop.  Likewise, don't expect to see ninjas jumping around next time you are in Yokohama.  Again, its fine to study history, just don't make the mistake of assuming that ancient Japan is the same as modern Japan.  Also, most Japanese people frankly don't care that much about the ancient past.  They are more likely to care about what cell phone models are hot this month, and who is on the top 10 music charts this week.  Older types tend to care about what time they can get off work to go drink, or which hot spring they can go to this weekend.  If you start talking about Rekishi or some such thing, don't be surprised if people look at you like you're crazy.  

Don't let all the cutesy Hello Kitty toys fool you, Japan has had some unfortunate events in its history, which people would rather not talk about.  In fact, bringing them up has cost more than one politician their career.

These are the people that have to do everything electronically, even if it costs them productivity.  Lost?  Why look at the map in your pocket?  Why ask the guy next to you?  No, fire up the GPS device.. even if it takes 10 minutes to get a lock much less enter your destination.  These people love Japan because they are constantly being bombarded by stories about how Japan is super high-tech, and robots do everything while the humans apparently nap all day.  Realistically, Japan and South Korea do put technology to better use than most of Europe and the US, but that's partly due to a willingness of consumers to pay.  If consumers will pay, companies can invest, and new services and products will be available sooner.  Yes, Japan does have better internet (both at home, and on the go), yes, the trains are better, yes there are lots of cool electronic devices.  Still, most of that is the logical result of investment.  It's not so much that Japan is ahead as it is that the US is behind.  Also, bear in mind that there are certain areas where Japan hasn't reached international first world standards just yet.  While half of the toilets are practically self-aware, the other half are basically a hole in the ground that you can flush.  I can also count the number of apartments I have seen with central heating and cooling on a single hand, with many places opting for the sweet smell of fresh kerosene instead.  Very few ATMs are 24 hours (which somewhat defeats the purpose of... using a machine, don't you think?).  Some of the trains look like something futuristic out of StarTrek, but there are also still some that look like they came from a WWII movie instead.  Just remember that they don't put the old/boring/missing stuff on the news.  Also, remember that while Akihabara is certainly cool, it is not representative of Japan.

You know who you are.  If you object when I call your favorite movie a "cartoon", or refer to your reading materials as "graphic novels" instead of comic books, then you are one of the above.  First of all, let's set the record straight.  Anime is a Japanese loan-word.  It is an abbreviation for "Animation", as in "Animated Cartoons".  It means "cartoon", that's how you would translate it into English.  If you are talking in Japanese, then アニメ (Anime) is fine.  If you want to speak Japanese, then speak your whole sentence in Japanese, and you won't be needing the subtitled version of the cartoon either, so until such time, it's a cartoon.  Likewise, "Manga" is Japanese for "Comic Book".  

Now, I don't think there's anything wrong with wanting to watch a cartoon or read a comic book now and again, but... some people are just obsessed.  I can tell this when they come up to me and say "Do you know the episode 43 of Naruto when the communist jellyfish monster comes out and rapes Hello Kitty with his tentacle?", etc. and provide details that I wouldn't possibly remember even if I had watched said cartoon.  Please, please understand, most Japanese people are not obsessed with Anime or Manga.  It may be slightly more popular than in the US, but slightly is.. well slightly.  Also, even those who do read so-called "graphic novels", most of them aren't so hard-core as you think, many simply want something to do besides fiddle with their phone on the train.

I think many people who are into this stuff overseas justify their unpopular pursuit by telling themselves, "It's ok, people here just don't understand, if I went to Japan I would be super-popular".  No, you wouldn't.  Again, most Japanese people aren't super crazy about comics or cartoons.  Ironically, the most popular cartoons in Japan are the ones aimed at the much younger demographic.  "Dr. Slump" and "Anpanman" get a lot more time than some strange Japanese cartoons over seas like "Captain BeBop" or "Naruto" ever will.  Why is this?  Well, primarily because the main audience for cartoons is children.  Cartoons aimed for an older demographic don't have as many customers.  On the other hand, if you don't live in Japan, I don't blame you for now knowing what's actually on Japanese TV.  I can tell you what usually isn't, tentacle porn.  

Furthermore, many of the anime/manga fans from outside of Japan tell themselves that all Japanese are similarly obsessed with comics and cartoons - and then they come to the mecca of all things dorky, Akihabara, and prove it to themselves.  Well, all I can say is that Akihabara is like Las Vegas, it's not representative of Japan in general - not by a long shot.  Most people have never been to a "Maid Cafe" either, for that matter.

Finally, the most extreme fringe is the group that do "cosplay", or "costume play", which is exactly what it sounds like.  [Frequently grown] people dressing up in costumes like it's Halloween.  Quite often they dye their hair to go with it.  Let me assure you that this is not normal behavior in Japan - it's just that all of the people who are into that sort of thing congregate in Akihabara.

On the other hand, I am not saying there is anything wrong with having interests in whatever entertain you - just realize everyone that not everyone else does, even in Japan.  Now that I've made you feel bad, go cheer yourself up by watching the movie about the dorky train man hero.

I say girl, because it mainly applies to girls, but sometimes guys as well (especially homosexual guys).  They've been shopping in Harajuku or similar, and are obsessed with tiny, cute, and shiny things - almost like a raccoon.  To them, Japan is all about what is cute.  Print clubs (where you make the small stickers), tiny hats, phone straps, cute overpriced clothes, etc. Well, that's all fine and well, but just know that while some women keep that up until they are well into their 30s, those are house-wives.  If you want to be taken seriously at work (or even graduate school), you're going to have to ditch all that.  Japan can be a great and fun place, but it's not Disney Land.