A character from one of Kirino's eroge. She has a fiery, mercurial temperament. As Kirino puts it, she is 100% tsun and 0% dere. Her twin sister is Miyabi, who perfectly contrasts Rinko's temperament with her mature, caring personality.
Rinko is supposed to be a representation of Kirino (and Rinko's relationship with the main character of the eroge is symbolic of Kirino's relationship with Kyousuke).