About Irimachi and Demachi
Irimachi is waiting for the Takarazuka stars to come to the theater before the first show of the day, and Demachi is waiting for them to leave after the last show is over.
"Wait!" you say. "What kind of obsessed weirdo would wait for the stars at the theater like that?"
Well, lots of perfectly normal people. Iri/demachi is a tradition in Takarazuka, and the star's fan clubs and a lot of other people always wait in front of the theater. The stars expect people to be waiting for them, and it's a daily ritual to greet fans and collect fan letters and presents.
Takarazuka fandom is very different from any other fandom I've ever been involved in. Stars are relatively accessable - you can take photos of them when they enter and leave the theater, they collect fan letters and presents from members of their fan clubs, attend special events put on by fan clubs, etc. In return, Takarazuka fans have a "code" of behavior which governs their actions. It is against the code to bother or stop the stars, ask them for autographs, follow them, etc.
There are other rules as well - such as which fan clubs get to stand closest to the stage door, etc. It can be hard to figure out these rules when you're a foreigner. In general, however, if you just do what everyone else is doing, you'll be alright.
General Guideline for Irimachi and Demachi
Irimachi: On most days stars arrive at the theater about an hour and a half before the first show of the day. But give yourself a little leeway - some stars may be quite early, while others may rush in just an hour before the show.Demachi: Stars start to leave about 30 minutes after the end of the last show of the day. It can take another hour for everyone to have left.
This is an "average" day - sometimes stars will leave late or come quite early, especially if something special is going on - like interviews, parties, etc. When I went to see retiring top-star Takumi Hibiki leave on her last day, I didn't end up going home until more than 3 hours after the show was supposed to have ended.
The rules for both irimachi and demachi are the same:
Don't bother the stars As I mentioned above, you shouldn't stop the star and ask her to pose for a photo, or ask for an autograph, etc. (This includes if you see her waiting for the subway later on.) You can only give her a fan letter or present if you ask her fanclub and get permission. However, it's perfectly alright to take photos of the star as she walks by and collects her letters.
Give way to the fan clubs Fan clubs get priority, and will line up along the sidewalk where the stars will pass by. Usually there are 2-3 rows of the fanclub members. Those not in a fanclub stand behind the clubs. If a fanclub officer asks you to move back a little, please do. Don't worry about seeing though. Whenever any star passes by, all the fanclubs will kneel down so that the people standing behind them can see. This isn't a "worship" thing - it's so you can get a good photo. :) The fanclub members themselves don't take photos.
Don't block the sidewalk This seems obvious, but the Japanese fans often forget it. Make sure there's room for innocent civilians to pass through. ;)
What Happens
There will be a lot of different fan clubs, probably wearing their club's shirt or jacket, lined up in front of the theater. The higher status or older the star is, usually the closer her club will be to the stage door. (Not always though.) The top stars usually arrive by car, and club officers will help by putting out orange cones and helping unload the car.Fan clubs for musumeyaku (players of female-roles) don't usually line up at the theater, although I've seen people waiting for the musumeyaku to come so they can give them fan letters.
Some stars are friendly, especially junior troupe members with small clubs, and stop to talk to their fanclubs and collect their letters and presents. Some stars will be tired at night or still sleepy in the morning, and may just wave at their clubs as they go by, especially if they're running late. In this case the letters are collected in advance by a club officer, and handed over to the star in a bag.
Stars often wear hats and/or sunglasses. This can be for any number of reasons - shyness, didn't have time to put on makeup, doesn't want to be blinded by all the camera flashes... As a photograph-taker I always liked it when stars didn't wear a hat or sunglasses, but I can understand why they often do.
Most stars wave to their fan club as they go in the building or drive off in their car. The whole club will then wave back, sometimes until the star is out of sight. At irimachi, the club often then moves out of the way so that the other clubs still waiting can spread out. At demachi, all the clubs wait until every star has left.
A Couple Tips
At demachi the best place to stand is across from the stage door - you can see everyone's face as they come out. OTOH, it's a bad spot at irimachi - all you see is the star's back as she goes in.
Try to stand behind the fan club of the star you most want to see - if she collects her own letters you'll have the chance to take photos from pretty close up. (A zoom lens helps too...) It can be hard to tell which fan club is which - but most clubs have their star's name or nickname on their "uniform" somewhere.
If you want to give a star a fan letter... You MUST ask an officer of her fan club for permission. In general, only fan club members are allowed to hand letters to the stars. But, some fan clubs are willing to make an exception if you're a foreigner. They may or may not ask you to join the fan club. If the club officer says no, or seems uncomfortable, just let the matter drop. (You can mail your letter to the theater instead.) FYI, although I've heard of people being told no, the 3 fan clubs I've talked to were all open and friendly with me.