Lonely
On the roof above, is a small stool. Anyone who sits in that stool will be lonely.
Imagine sitting on this small stool, waaaaay up there above the roof. You can't see anyone and you can't talk to anyone. You feel this awful emptiness inside. That's what it's like to be lonely.
じゃく, せき
さび, さみ
None
You're so lonely, you make up an imaginary friend: Jack (じゃく). Jack doesn't get rid of the lonely feeling because he isn't real, but he is a distraction at least.
You're so busy talking to Jack, you don't hear the voices from below, "Aren't you lonely up there, miss? Do you want us to get a jack to get you down? Hello? I don't think she can hear us..."