In Japanese, when one says daiya (ダイヤ), it could mean two things.
One is short for diamond, as in precious gem. The other is short for diagram, and more precisely, refers to a service planning diagram used in railway and bus operation.
Daiya in latter case is a document showing exact routes and time schedules of public transportation. When you are using trains in Japan, sometimes you may hear announcements for “daiya no midare (ダイヤの乱れ).” It means daiya, or the pre-set operating plan, has been disrupted, and certain trains and buses may be delayed as a result of it.
Daiya could be disrupted by various reasons, such as bad weather, accidents, and natural disasters. When it happens, railway companies are not responsible for financial loss caused by delay, so they wouldn’t be able to pay your tickets back. What they can do though is to issue a certificate of delay (Chien Shoumeisho from Japan Word of the Day #44) that you can bring to work to legitimately explain why you were late.
If you are going to spend a prolonged period of time in Japan, teikiken (定期券) will come in handy. Teiki means periodic, and ken means a ticket. It’s a special type of railway pass you can use repeatedly within a certain period for a specific route (between pre-specified train stations). The price for teikiken is discounted and will end up cheaper than if you were to buy tickets individually. You can usually get teikiken with different time durations, 1 month, 3 months, abd 6 months.
There are many kinds of teikiken, but the most common ones are Tsūkin(Work), Tsūgaku(School), and Tokubetsu Sharyou(Special Train).
通勤定期(Tsūkin Teiki): For people who take the same train route for work. However, it doesn’t require any proof of your workplace, so in reality, you can purchase it for any purpose beside work.
通学定期(Tsūgaku Teiki): For students who take the same train route for transportation between their home and school. You’ll need to show proof of your enrollment to schools to purchase this pass.
特別車両定期(Tokubetsu Sharyou Teiki): This is for people regularly taking special trains that offer Green Cars (premium class seats), including Shikansen and special rapid lines such as Shonan Shinjuku Line, Airport Narita Line, etc.
You can either buy them in traditional magnetized pass, or in SUICA pass format. Or if you have cellphones in Japan, you can even have one on your phone!
For JR, you can purchase teikiken at ticketing machines at JR stations or at Midori no Madoguchi Ticket Offices.
The Okayama brunch of Japan Railway West is selling ekiben lunch set featuring NARUTO! Ekiben is boxed lunch usually sold on trains and train stations. Okayama, because the author of NARUTO Masashi Kishimoto is from this prefecture, has been holding a series of promo campaigns in collaboration with NARUTO this year, and this is part of them.