Grass radical at top marks 芮 originally as a small water-grass (a kind of duckweed or sedge). Same plant-cap radical drives 花, 草, 菜. As a surname it traces back to the small Zhou-era state of Rui (芮国), located in modern Shaanxi.
内 supplies the sound — nèi → ruì — through an Old Chinese onset shift between dental nasal and retroflex. Faintly hints at smallness: 芮 originally meant a small inner stream-grass. Same phonetic also appears in 纳 (nà), 呐 (nà), and the surname 芮 itself.
