宙 is a Japanese kanji written with 8 strokes, listed here under the keyword “mid-air”. It is built from 宀 (roof) and 由 (wherefore). In Remembering the Kanji by James W. Heisig it is frame 1190.
On KumiJi Glyph Explorer, open the parts search and type “roof” + “wherefore”. 宙 is among the results, together with every other character containing the same shapes.
Open 宙 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.