[quote=Lennon79]
Adding -nii to the end if a name implies that the person is an older brother; I thought Shiori was older O_o
[/quote]

If it's just -nii, it means younger brother. If it's -onii, though, it's older brother. Yuusuke calls Shiori onee-chan because that means older sister. Likewise, nee-chan means younger sister.