This Sunday, do you want to go to that store we talked about earlier?

Sunday?

Ah, sorry, I can't. I promised my younger sister we'd go shopping.

What's with that look...

She's the enemy.

What are you competing over...

Just because she's your sister, I can't be unprepared. I already warned her about this before, but she shouldn't be sleeping together with you.

Ah, sometimes she sleeps with me.

She's in for it next time I see her.