瑟 is a Chinese hanzi, listed here under the keyword “large stringed musical instrument”. It is built from 玨 (two pieces of jade joined together) and 必 (surely). It appears as a component in 3 other characters in this index.
On KumiJi Glyph Explorer, open the parts search and type “two pieces of jade joined together” + “surely”. 瑟 is among the results, together with every other character containing the same shapes.
Open 瑟 in the interactive kanji search
to expand every part down to its smallest pieces, add your own names and mnemonic stories,
or search for other characters by their parts.