Saki Mishima, referred to as Miss Saki, stands as both adoptive sister and enigmatic figure in Yusuke Ninomiya’s life. Their familial ties remain ambiguous—whether bound by shared adoptive parents or a guardianship masked as sisterhood. She runs a quaint flower shop in her hometown and shares an unexplained soulmate bond with Bertha Roam.

When a Black Banner Assassin infiltrates her shop, morphing into a monstrous spider mid-pursuit, Saki narrowly escapes by plunging her car into a raging river alongside Yusuke and Haru. This encounter unravels a larger threat: interdimensional forces destabilizing reality itself.

After Galeroth’s defeat and Yusuke’s choice to remain in the other world, Saki’s memories of him dissolve completely. The erasure spreads universally, leaving Haru as the lone keeper of Yusuke’s legacy. Beyond these events, her story concludes without elaboration.