She's a serious and calm girl that's at 'Empty Sekai'. The Sekai are created with a person's feelings, in this case, the place is Empty.
Rin uses to have a "neutral" relationship with all of the integrants (Mizuki Akiyama, Kanade Yoisaki, Ena Shinonime And mafuyu Asahina). They aren't Vocaloids
She has a brother named 'Len Kagamine', but he's a bit timid... Meiko is almost the same, a serious person, along with Kaito.
The other are Hatsune Miku and 'Megurine Luka'.
...No, I'm not worried for you