I'm not fooling around! [He snaps, voice suddenly too loud in the empty space. He doesn't have time for something so frivolous. And then Rin keeps talking, and it's so obvious that Rin apparently does have time for fooling around.

Why is his brother like this? Why does Rin keep doing this to him?]

Of course I asked for something important! It would be stupid to contract with a demon for anything less!