Several parts combine into one character.

義 is a compound ideograph: 羊 (sheep) on top + 我 (wǒ, "I / me" — originally a serrated battle-axe pictograph) on the bottom. The composite scene is sacrificial: a ceremonial axe carefully dividing a sacrificial sheep for ancestral rites — performing the ritually correct action with proper reverence. From this concrete ritual origin grew the abstract sense "righteousness, the morally correct, what one ought to do, justice." 義 became one of the four cardinal Confucian virtues alongside 仁 (benevolence), 礼 (propriety), and 智 (wisdom). Mainland China simplified to 义, removing both components and replacing them with two strokes — one of the most aggressive simplifications in the entire reform.

Korean reading "ui." This single character anchors East Asian moral vocabulary: 正義 (jeongui, justice), 義務 (uimu, duty / obligation), 主義 (juui, "-ism" / doctrine), 義兄弟 (uihyeongje, "righteous brothers" = sworn brothers), 信義 (sinui, fidelity / good faith), and especially 義理 (uiri, loyalty / sense of obligation — a culturally loaded Korean concept that goes deep into popular culture, mafia tropes, and high-school friendship vocabulary; Korean dramas treat 의리 as a near-untranslatable virtue of standing by one's associates through hardship). 의리 entered colloquial Korean speech: (to have integrity/loyalty).

Mandarin yì, 4th tone (simplified 义). 意义 (yìyì, "meaning-significance" = meaning), 正义 (zhèngyì, justice), 主义 (zhǔyì, "-ism" — used for ideological labels: 资本主义 capitalism, 社会主义 socialism, 民族主义 nationalism), 义务 (yìwù, obligation), 义气 (yìqì, sense of brotherhood / bro-loyalty — the gangster-honor concept that translates roughly to Korean 의리). The pattern Noun + 主义 generates the entire modern Chinese vocabulary of political and philosophical positions.

Japanese on-reading ギ (gi) — 義務 (gimu, duty / obligation), 正義 (seigi, justice), 主義 (shugi, doctrine / ideology), 義理 (giri, social obligation — central to Japanese culture), 定義 (teigi, definition). Most distinctly Japanese cultural compound: 義理チョコ (giri-choco, "obligation chocolate") — the Valentine's Day chocolates Japanese women give not out of love but out of social obligation to male coworkers and acquaintances. Distinguished from 本命チョコ (honmei-choco, "true-feeling chocolate") given to a romantic interest. The giri/honmei distinction is uniquely Japanese — chocolate diplomacy as social grammar.

Memory aid: a sheep (羊) above an axe (我) — performing the ritually correct sacrifice = righteousness.