Ruri is actually a pretty minor character. ^_^;  She's Sara's friend, a shy, quiet, glasses-wearing girl with the ability to see auras.  Her name (as Rociel tells her) refers to 'Lapis Lazuli', a very beautiful blue stone. ^^  Ruri falls in love with Setsuna and asks Sara to help her, and Sara reluctantly agrees (though she really doesn't like the idea because she is also in love with Setsuna ^^;), but things get messed up when the three are attacked in a church.  Setsuna protects Sara, but glass fragments shower over Ruri, permanently destroying her eyes. She's confined to her bed, with pretty much only her computer for company.  The computer has the 'Digital Angels' CD inside it, given to her by Katan.  Once it was activated, it began talking to Ruri and  invading her subconscious.  It (or rather, Rociel) drains all of Ruri's energy and allows Rociel to possess her body, leaving a very changed Ruri behind. ^^;

I felt really bad for Ruri--she was a really sweet girl, and then she goes and gets possessed and dies. ><;