後輩
こうはい
kouhai
= junior / younger colleague at school or work
Everyone who has heard of senpai assumes it stands alone, but the word only makes sense because kouhai exists on the other side of it. A kouhai is the junior member of a school, club, or company who joined after you did, and without this half of the pair the whole senior-junior system Japan is famous for would collapse.
The kanji spell it out plainly: 後 means “after” and 輩 means “peer” or “fellow,” so a kouhai is literally a fellow who came after. What makes this word tricky for learners is that it has nothing to do with age. A 30-year-old who joins a company where a 22-year-old has worked for three years is that 22-year-old’s kouhai, full stop. Entry date decides everything. The relationship also runs both directions: a senpai is expected to look out for their kouhai, teach them the ropes, and often pick up the bill after work, while a kouhai is expected to speak politely upward, ask for guidance, and generally defer to the senpai‘s experience even if the kouhai personally knows more about the task at hand.
One mistake learners make is trying to call someone “kouhai” the way they’d call a senior “senpai-san.” It doesn’t work that way — kouhai almost never gets used as a direct term of address. You’d call a junior colleague by their name, frequently with -kun or -chan attached, not by the label “kouhai.” Where the word shines is in third-person description: saying uchi no kouhai (“my kouhai” / “a junior of mine”) is completely natural when introducing or talking about someone. Also worth knowing: the bond doesn’t expire when people change jobs or graduate. Someone who was your kouhai in a college club can still greet you as their senior twenty years later at a chance reunion, even if neither of you ever crosses paths with that club again.
Everyday use
こちら、うちの後輩の田中です。
Kochira, uchi no kouhai no Tanaka desu.
This is Tanaka, a junior colleague of mine.
Casual / Social Media
今日の飲み会、後輩が全部セッティングしてくれた。頼りになる！
Kyou no nomikai, kouhai ga zenbu settingu shite kureta. Tayori ni naru!
My junior arranged today’s whole get-together. So reliable!
Formal / Cultural context
日本の会社では、入社した年によって先輩と後輩の関係が決まります。
Nihon no kaisha de wa, nyuusha shita toshi ni yotte senpai to kouhai no kankei ga kimarimasu.
At Japanese companies, the senpai-kouhai relationship is determined by the year someone joined.
The senpai–kouhai system is one visible layer of what sociologists call Japan’s tate shakai, or “vertical society” — social groups organized by rank and seniority rather than by age or skill alone. From the moment you join a company, sports team, or club, your position relative to everyone else is fixed by your entry date, and that ranking quietly shapes how people speak to each other, who serves tea at meetings, and who gets asked to run errands.
School and university sports clubs are widely considered the strictest training ground for this hierarchy. First-year kouhai are often assigned tasks like carrying equipment, cleaning the practice space, or greeting every senpai loudly in the hallway, and stories of especially rigid clubs are common enough that the word kouhai carries a faint memory of hazing-like discipline for many Japanese adults, even those who never experienced it firsthand.
Outside the club room, though, the tone is usually far gentler, and it keeps getting gentler. Many modern startups and flatter-structured companies actively downplay the strict duties once expected of a kouhai, preferring first-name-adjacent casualness over rigid deference. Still, the underlying concept never really disappears — even in the most relaxed office, people quietly track who arrived first.