Several parts combine into one character.

Phonetic-semantic compound with poetic etymology: 氵 (water) + 每 (originally derived from 母, mother — providing both phonetic value and semantic suggestion). The encoded image: "the great water that, like a mother, receives all rivers". 海 sits at the largest end of the CJK water-size hierarchy: 川 (small stream) → 河 (river) → 江 (great river) → 海 (sea / ocean). Identical across 繁體 / 新字体 / 简体.

Mandarin: hǎi, dipping 3rd tone. 海 anchors maritime vocabulary: 海洋 (hǎiyáng, ocean), 海岸 (hǎi'àn, coast), 海军 (hǎijūn, navy), 海鲜 (hǎixiān, seafood — "sea-fresh"), 海带 (hǎidài, kelp), 海归 (hǎiguī, "sea-returner" — Chinese students who studied abroad and came back). The city 上海 (Shànghǎi) literally means "above-sea / by the sea". The Yellow Sea (黄海) and East China Sea (东海) define China's eastern boundary.

Japanese: on-reading カイ (kai) for compounds — 海洋 (kaiyō, ocean), 航海 (kōkai, voyage), 海軍 (kaigun, navy), 海岸 (kaigan, coast). Kun-reading うみ (umi) is the everyday word — 海 (umi, sea), 海辺 (umibe, seaside), 海鳥 (umidori, sea bird). Japan, surrounded by sea, deploys 海 vocabulary heavily — 海女 (ama, female pearl divers, an iconic Japanese cultural tradition), 海苔 (nori, seaweed sheets — for sushi), 海老 (ebi, shrimp/lobster — irregular reading meaning "sea-old").

Note 北海道 (Hokkaidō) — Japan's northernmost prefecture — combines 北 + 海 + 道, literally "Northern Sea Road".

Memory aid: water + mother — the great water that receives every river.