兄弟
きょうだい
kyoudai
= siblings / brothers / brothers and sisters
兄弟 (kyoudai) means siblings — but Japanese has one of the world’s most elaborately differentiated family vocabulary systems, where the word you use for a sibling depends on whether they are older or younger, male or female, and whether you are referring to your own family or someone else’s.
Kyoudai broadly means brothers or siblings. It can refer specifically to brothers (male siblings) or more broadly to all siblings of mixed or unspecified gender. For precision, Japanese uses: 兄 (ani — older brother, referring to one’s own), お兄さん (onii-san — older brother, addressing or referring respectfully), 弟 (otouto — younger brother), 姉 (ane — older sister, one’s own), お姉さん (onee-san — older sister, respectful), 妹 (imouto — younger sister). 姉妹 (shimai) means sisters specifically. 兄弟姉妹 (kyoudai shimai) is the formal all-inclusive term for all siblings.
Japanese family vocabulary distinguishes in-group (自分の家族, jibun no kazoku — one’s own family, spoken of humbly) from out-group (他人の家族, tanin no kazoku — another’s family, spoken of respectfully). When speaking of your own sibling, use 兄 (ani), 弟 (otouto), 姉 (ane), 妹 (imouto) — plain forms. When speaking to or about someone else’s sibling, use お兄さん (onii-san), 弟さん (otouto-san), お姉さん (onee-san), 妹さん (imouto-san) — with さん.
兄 (ani/kei) means ‘older brother.’ 弟 (otouto/tei/dai) means ‘younger brother.’ Together as 兄弟 (kyoudai): brothers/siblings — the combination represents the full range of sibling relationships.
Everyday use
私には兄弟が3人いて、兄が2人と妹が1人います。
Watashi ni wa kyoudai ga san-nin ite, ani ga futari to imouto ga hitori imasu.
I have three siblings: two older brothers and one younger sister.
Casual / Social Media
兄弟ってケンカするけどやっぱり一番信頼できる存在だよな
Kyoudai tte kenka suru kedo yappari ichiban shinrai dekiru sonzai da yo na
Siblings fight but when it comes down to it they’re the ones you can trust the most
Formal / Cultural context
少子化の進展に伴い、一人っ子世帯の増加により兄弟姉妹を持たない子どもの割合が高まっており、兄弟関係を通じた社会性の育成機会が減少しているとの指摘がある。
Shoushika no shinten ni tomonai, hitorikko setai no zouka ni yori kyoudai shimai wo motanai kodomo no wariai ga takamatte ori, kyoudai kankei wo tsuujita shakaisei no ikusei kikai ga genshou shite iru tono shiteki ga aru.
With the advance of declining birthrates, the proportion of children without siblings is rising due to increased single-child households, and there are observations that opportunities for developing social skills through sibling relationships are decreasing.
Japanese family vocabulary (家族の呼び方, kazoku no yobikata) is one of the most complex and culturally revealing aspects of the language. The elaborate system of different terms for older vs younger, in-group vs out-group, and gender-specific relationships reflects values of hierarchical respect, humility about one’s own family, and deference toward others’ families. A learner who masters when to say 兄 (ani) vs お兄さん (onii-san) has understood something deep about how Japanese people position themselves relative to others.
In Japanese popular culture, 兄弟 relationships are a major narrative theme. The dynamic between older and younger siblings — the responsible older (兄 or 姉), the free-spirited younger (弟 or 妹) — appears constantly in anime, drama, and literature. Specific archetypes like 毒親 (dokushin — toxic parents in sibling rivalry narratives) and お兄ちゃん系 (onii-chan-kei — the protective older brother character type in romance manga and games) reflect how sibling dynamics are processed and mythologized in Japanese storytelling. The honorific onii-san and onee-san are also used by younger characters for older unrelated characters to signal respect and closeness — a social use of sibling terms beyond actual family relationships.
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