Hot
Hot Weather
If the sun is on someone, they will get hot. That's just how it is. Someone standing out in the sun for a long time will inevitably get hot. The sun is hot, and it makes you get hot too.
Note that this usually refers to hot weather or the heat of an area you're in and doesn't refer to a hot "thing."
しょ
あつ
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One sun was hot enough, but then a second one shows up. "Ah, two (あつ)!" you scream. If you were sweaty and sticky from the heat of just one sun, imagine what this second one is going to do to you. Ah, two hot suns!