う
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You use a roof to keep yourself dry and safe from outer space. Look outside, above your roof, and you'll see outer space stretching above you.
Why isn't it dry in outer space, you ask? Because of all the uni (う) swimming around up there. They have nasty, wet, pointy spikes and they're all over the place.
Currently there are no similar looking kanji which exist in the WaniKani learning system