Several parts combine into one character.

Phonetic-semantic compound: 忄 (heart-radical, the left-side variant of 心) + 生 (to be born). The encoded meaning: "the heart one is born with" → innate nature / character / disposition. The character later expanded to mean "type of thing" (性質, properties of an object) AND "biological sex" (男性, 女性). Three meanings unified by "innate identity". Identical across 繁體 / 新字体 / 简体.

Mandarin: xìng, falling 4th tone. 性格 (xìnggé, personality / character), 性别 (xìngbié, gender), 性质 (xìngzhì, nature / property of something), 男性 (nánxìng, male), 女性 (nǚxìng, female), 性能 (xìngnéng, performance / capability — used for products), 个性 (gèxìng, individuality), 重要性 (zhòngyàoxìng, importance — abstract noun suffix "-ness"). The 〜性 suffix is highly productive in modern Chinese for forming abstract nouns.

Japanese: TWO on-readings. セイ (sei) is dominant — 性格 (seikaku, personality), 性別 (seibetsu, gender), 個性 (kosei, individuality), 性能 (seinō, performance), 男性 (dansei, male), 女性 (josei, female). ショウ (shō) appears in 本性 (honshō, true nature), 相性 (aishō, compatibility — used in dating, business: "good 相性" = a good match). Kun-reading さが (saga) is poetic / archaic — 人の性 (hito no saga) "the way humans are" appears in literature.

The 〜性 suffix in Japanese (and 性 / xìng in Mandarin) is one of the most productive abstract-noun-forming suffixes — like English "-ness" or "-ity": 重要性 (jūyōsei, importance), 可能性 (kanōsei, possibility), 必要性 (hitsuyōsei, necessity).

Memory aid: heart + birth = the disposition you're born with.