KanjiJLPT N1
Mid-Air

mid-air, air, space, sky, memorization, interval of time

Mnemonic

Your roof rips away and flies upward. The reason? A vortex in the sky! You grab the roof's edge, now dangling in Mid-Air with no ground beneath you. There's no reason to look down — just hold on and float among the stars.
Additional thoughts
Visualize clinging to your roof as it rockets into the cosmos. The reason it launched is a mystery — all you know is you're suspended in open space. Roof + Reason = Mid-Air.
Quick recall
A roof launches skyward for no reason, leaving you dangling in Mid-Air.

Details

The keyword for 宙 is mid-air. This kanji refers to the space between heaven and earth, the open air, or the void above the ground. It conveys the sense of being suspended in space, floating, or hanging without support. It is often associated with the concept of the cosmos or outer space, as well as the state of being up in the air, both literally and figuratively.
On'yomi
ちゅう