O.L.: "Office Lady", female office worker who serves tea, cleans desks, etc. Bluntly put, office wives.
Salaryman: White collar office worker.
Genkan: The entryway of a Japanese home. This is where you take your shoes off, put on slippers, and (usually) step up into the house.
Oneechan: Affectionate term for one's older sister. Pronounced "oh-nay-chan". Also used to refer to any young woman older than oneself. It's not used in this story, but Oniichan ("oh-knee-chan") is the equivalent term for an older brother. If you're being more formal, it's "Oneesan" and "Oniisan".
imouto: little sister. The equivalent for little brother is "otouto".
Katana: A Japanese sword.
Bokken: A wooden practice sword, used in Kendo.
Kendo: Martial art using wooden practice swords.
Kenpo: The Japanese word for Kung Fu, a martial arts style.
Kotatsu: Many Japanese homes (especially traditional styles) do not have central heating. A kotatsu is like a table with a heater underneath it, and which has a fabric skirt. You sit with the lower part of your body underneath the skirt to warm up.
o-miyage: Souvenirs from a trip. It's pretty much mandatory to bring these back to people at home and at the office when you go on a trip.
Yatai: a portable restaurant cart. The vendor takes it to a location, puts out stools (usually there's just room for two or three) and sometimes curtains for a little privacy. Instant restaurant.
Itte kimasu/itte 'rasshai: Set phrases used when leaving home (roughly equivalent to "Goodbye" and "See you when you get back")
Tadaima/O-kaeri (nasai): Set phrases used when coming home (roughly equivalent to "I'm back" and "Welcome home")
Ohayou (gozaimasu): Good morning.
O-yasumi (nasai): Good night. Used only when parting for the evening, or with family, going to bed.
Itadakimasu: Literally, "I humbly receive." Always said before meals, even if the meal is a Cup Noodles eaten alone.
Yatta: Exclamation meaning "I did it!" (even if the speaker didn't actually do it), also used in similar ways to "all right!" or "Yessss!"
Mou: Literally, "already". Can be used as a frustrated exclamation: "Mou iya da!" (I'm sick of this already), or just "Mou!" When used by itself, most often used by women.
Ganbatte (kudasai): A set phrase to encourage someone. "You can do it," "Go for it," "Good luck."
ne: Japanese sentence ending soliciting agreement. Like "isn't it?" or "don't you think?" in English. Example: "ii o-tenki desu ne." (Nice weather, isn't it?)
Baka: The all-purpose Japanese insult. Idiot, fool, moron, etc. Used by both men and women.
(name) no baka: "(name), you idiot! Again, used mostly by women. Men use nastier insults.
Gomen (nasai): "I'm sorry". Most often used by women.
Kantou: The large, flat plain where Tokyo is located. Literally, "Eastern Plain". "Western Plain" is Kansai, where Osaka, Kyoto, and Kobe are located. Ukyou is from Kansai and speaks a dialect (Kansai-ben) in the original Japanese.
Okami-san: The wife of the owner of a business. Usually responsible for the bookkeeping, often helps in the actual work. Cooks meals for any apprentices as well as for the family, and does similar, traditionally female chores for the business. Never gets paid a dime, of course. ;-)
Terms of address (simple version):
-san: like Mr., Ms., etc. Everyday polite usage.
-sama: extremely polite version of "-san", used for superiors, or when you want to be extra-polite. More often used by women.
-sensei: Master, Teacher, Doctor. Term of respect.
-kun: Refers to an inferior of either sex, or to a boy.
-chan: Suffix indicating endearment (see "Oneechan", above). Also used to refer to girls (but not women), or a very young child of either sex. Used by childhood friends (e.g., Ranchan, Ucchan).
Kami-sama: God