Otsukaresamadesu

The single most-used phrase in Japanese workplaces. Literally means something like "you must be tired (from working hard)," but in practice it has lost most of that meaning and functions as a universal greeting. Use it instead of "hello" anytime after morning, when leaving work (お疲れ様です/でした), at the start of emails, or just passing someone in the hallway. Casual forms: "おつ" (otsu) and "おつかれー" (otsukare-). Important: the similar-sounding "ご苦労様" (gokurousama) is strictly top-down — a boss can say it to their team, but never use it toward a superior. Also, お疲れ様です is mostly for people within your own company or team. For external contacts (clients, partners), use "お世話になっております" (osewa ni natte orimasu) instead, which roughly means "thank you for your continued support" — though like お疲れ様です, it is mostly just a formality.