Shiori Sekine (栞関根, Sekine Shiori) is the bassist of Girls Dead Monster, with a G&L L-2000 bass guitar as her playing instrument and Hartke HA3500 or 5500 (external aesthetics identical) as her amp, she likes to play pranks on those around her to see the surprised faces of her victims. She also likes to abruptly improvise during performances, which makes Hisako get mad at her. She is best friends with Irie, whom she calls "Miyukichi" and both of them joined Girls Dead Monster at the same time. Although she isn't good at playing the bass, Hisako stood up as her guide during their practice performances. She is also seen singing backup for Iwasawa when the band first performed "Crow Song" in the anime.
- Sekine was a contestant of the voting contest Anime Saimoe Tournament 2010 but lost to Mio Akiyama in the first round of the main tournament.
- She has the same name with the only female member of the band Base Ball Bear.
- Like Yusa Nishimori from Charlotte. She has a long blonde hair and blue eyes.