Ran Otonashi (音無 蘭, Otonashi Ran?) is the oldest of the three Otonashi Siren sisters and is revealed to be very shy around boys and is also an otaku (both formal and informal Japanese word or term for "nerd" or "geek", literally someone (Japanese person) who loves a lot of manga books, anime animation, and/or merchandise in Japan and loves to personally buy them); as it is mentioned that she reads BL (boys' love or yaoi, pronounced as yah-oi in Japanese, not yow-i) and Shōjo manga (girls specifically targeted to young adult girls or the Japanese word, literally meaning "girl" but specifically being a term for a milestone age in young adult women). She is also officially the nerdiest and geekiest sister of the group being an otaku and the only otaku.
- Ran appears exclusively in Rosario-Vampire Capu2: The Rhapsody of Love and Dreams and is part of a group of Sirens who are attempting to gain the affection of all the boys in school with their abilities.
- Despite having the same last name, Ran is not related to San Otonashi.
- She, Ren, and Rin are Siren sisters.