What burns

社 has 示 (altar / to show) for meaning and 土 (earth) lending both sound and sense. It originally meant an altar of heaped earth (土) for worshipping the god of the local soil — the place where villagers gathered to sacrifice to the land-spirit. From that gathering grew the sense "association, society, organization."

Korean hanja-sound "sa": 會社 (hoesa, company), 社會 (sahoe, society), 社長 (sajang, company president), 新聞社 (sinmunsa, newspaper company). Strikingly, the same two characters reversed give 會社 (company) and 社會 (society).

Mandarin: shè, 4th tone. 社会 (shèhuì, society), 社区 (shèqū, community / neighborhood), 社交 (shèjiāo, social interaction), 合作社 (hézuòshè, cooperative). Note that "company" in Mandarin is 公司 (gōngsī), not 社.

Japanese: on-reading シャ (sha), kun やしろ (yashiro). 会社 (kaisha, company), 社会 (shakai, society), 神社 (jinja, Shinto shrine), 社長 (shachō, company president). The kun やしろ means a shrine housing a god, keeping the original sense (an altar to the soil-god) alive.

Memory aid: earth (土) beside an altar (示) — where people gathered to sacrifice to the god of the land.

聲 (traditional) was originally a picture of striking a 磬 (a stone chime) plus 耳 (ear) — the upper 殸 is a hand with a mallet striking a stone instrument, the lower 耳 is the ear hearing it. From an instrument's sound reaching the ear came "sound, voice." The shinjitai and simplified kept only the upper part, greatly reducing it to 声.

So the form splits: traditional (ko/en/es) is 聲, shinjitai (ja) and simplified (zh) are 声 — a sharp difference in stroke count (聲 17 vs 声 7).

Korean hanja-sound "seong": 音聲 (eumseong, voice / audio), 聲帶 (seongdae, vocal cords), 名聲 (myeongseong, fame), 歡聲 (hwanseong, cheers), 聲明 (seongmyeong, a statement). Korea uses the traditional 聲.

Mandarin: shēng, 1st tone. 声音 (shēngyīn, sound), 大声 (dàshēng, loud), 声调 (shēngdiào, tone), 相声 (xiàngsheng, crosstalk comedy), 名声 (míngshēng, reputation). It is the 声 of the four tones of Mandarin — 第一声 (the first tone).

Japanese: on-readings セイ (sei) and ショウ (shō), kun こえ (koe) and こわ (kowa). 声 (koe, voice), 音声 (onsei, voice / audio), 声優 (seiyū, voice actor), 歓声 (kansei, cheers), 名声 (meisei, fame). Before a compound こえ shifts to こわ — 声色 (kowairo, tone of voice).

Memory aid: striking a stone chime heard by the ear — the traditional has the ear (耳), the shinjitai keeps only the top.

火 pictures rising flames — a central plume with two flickering tongues at the sides. Identical across 繁體 / 新字体 / 简体. Like 水, 火 has a critical positional variant: when it appears at the bottom of a character, it flattens into 灬 (four dots, called the "fire-foot" radical). Once you spot 灬 you can predict heating or cooking: 熱 (hot), 煮 (boil), 焦 (scorched), 烈 (intense), 然 (originally "burn", now mostly grammatical). The four dots are not water — they are fire seen from above.

Mandarin: huǒ, dipping 3rd tone. 火 alone is fire; 火车 (huǒchē, "fire vehicle") is a train, named in the steam-engine era and never updated; 火山 (huǒshān) is volcano; 火锅 (huǒguō, "fire pot") is hot pot, the communal Sichuan meal.

Japanese: on-reading カ (ka) in 火曜日 (kayōbi, Tuesday), 火災 (kasai, fire/blaze), 花火 (hanabi, fireworks — literally "flower-fire"). Kun-reading ひ (hi) — same syllable as 日 (sun), so context disambiguates. Note the planetary week: Tuesday is "fire day", named for Mars (the Mars/fire planet) in the East Asian system that parallels the Western Tuesday-from-Tiu.

Memory aid: a vertical flame with two side sparks. If you ever see four small dots running across the bottom of a character, mentally translate "fire underneath".