弟
おとうと
otouto
= younger brother
弟 (otouto) is the Japanese word for your own younger brother — a term that carries the weight of seniority-conscious family culture, where the exact position of each sibling in the birth order shapes how everyone speaks and relates to one another.
弟 refers exclusively to one’s own younger brother. This in-group restriction is fundamental: when speaking about someone else’s younger brother, you must use 弟さん (otouto-san) as a mark of respect toward the other family. Using 弟 alone for another person’s sibling would sound dismissive or even rude.
In humble speech (謙譲語, kenjougo), a speaker always refers to their own sibling with the plain form 弟, never attaching honorific prefixes. This mirrors the broader rule in Japanese that you speak “down” about your own family and “up” about others’.
Gender distinction is strict: 弟 is male only. A younger sister is 妹 (imouto). For the older counterpart, 兄 (ani) means one’s own older brother and お兄さん (onii-san) is used for someone else’s.
While 弟 is the formal or referential label, within a family 弟 is rarely used as a direct form of address. Parents and siblings usually call a younger brother by his given name or a nickname. The word 弟 surfaces mostly when introducing or describing him to outsiders.
The most common mistake for learners is using 弟 when talking about someone else’s younger brother. Always switch to 弟さん in that case. Conversely, adding さん to your own sibling (弟さん about yourself) sounds unnatural and overly formal in Japanese.
Another point of confusion is pitch accent: 弟 (otouto) has a distinctive pitch pattern (LHH↓L in Tokyo dialect) that differs from 妹 (imouto) (LHHL). Mixing them up in speech, especially when speed increases in conversation, is a frequent error.
In casual writing and texting, some younger speakers write おとうと in hiragana rather than the kanji, but 弟 remains standard in any formal or semi-formal context.
The character 弟 traces back to the pictograph of a cord wound spirally around a stake or peg. The winding represents sequential order from top to bottom — each layer coming after the one above it. From this image of ranked succession, 弟 came to denote someone who comes after in birth order, i.e., a younger sibling. The same root gave rise to 第 (dai), the ordinal prefix seen in 第一 (first), reinforcing the core idea of sequence and rank.
Everyday use
弟は今3歳なので、まだひらがなしか読めません。
Otouto wa ima san-sai na node, mada hiragana shika yomemasen.
My younger brother is three years old now, so he can only read hiragana yet.
Casual / Social Media
弟とゲームで喧嘩した😂またやらかした
Otouto to geemu de kenka shita 😂 mata yarakashita
Got into a fight with my little brother over a game 😂 did it again lol
Formal / Cultural context
先日はわたくしの弟が大変お世話になりまして、誠にありがとうございました。
Senjitsu wa watakushi no otouto ga taihen osewa ni narimashite, makoto ni arigatou gozaimashita.
Thank you very much for taking such good care of my younger brother the other day.
Japanese family culture is structured around the concept of 年功序列 (nenkoujoretsu) — seniority by age. A younger brother (弟) occupies the lowest rung among brothers, which shapes everyday dynamics in concrete ways. Older siblings are expected to set an example and may shoulder more responsibility, while the 弟 is often given more latitude and affection as the youngest male. This dynamic even appears in how chores and curfews are negotiated: it is not unusual for a 弟 to be held to looser rules than his older siblings, sometimes generating good-natured resentment from the 兄 (ani).
The stereotypical image of the youngest brother in Japanese media and everyday conversation tends to split into two contrasting archetypes: the pampered, easygoing 末っ子 (suekko, youngest child) who charms his way through life, and the driven younger sibling who feels constant pressure to distinguish himself from an accomplished older brother. Both archetypes reflect the real social weight that birth order carries in Japanese households, where family role — not just personality — shapes expectations from childhood through adulthood.