"Rin, was that idol girl lying to your questions?" A deep and calm voice suddenly broke the silence of the room.
"No, she honestly answered all my questions." Rin replied to the girl.
"I see, so is yua innocent?" The girl asked while she was working in a computer.
"Never"
Rin replied with a sneer on his face.
"If that's the case, why don't we just conduct a lie detecting test or something like that on her?" The girl asked even though she already is aware of rin's answer.
"That would just end the whole case! Just when the case became amusing, you recommend me something so pathetic?
That is so like ya." Rin replied being dissatisfied.
"So, that means you will let people die and enjoy everything yourself? Rin, you are rin." The girl replied but this time her voice became deeper than that of before.
Meaning of the title;
'Sour and bitter' respectively refers to rin and the girl he was talking to, rin bringing sourness to the story and the girl bringing bitterness to the story.
Other;
Rin, you are rin.- As mentioned earlier rin means cold, so the meaning of the phrase is 'Rin, you are cold.'