界 is a Chinese hanzi, listed here under the keyword “boundary”. It is built from 田 (field) and 介 (forerunner). It appears as a component in 4 other characters in this index.
On KumiJi Glyph Explorer, open the parts search and type “field” + “forerunner”. 界 is among the results, together with every other character containing the same shapes.
Open 界 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.