Hokuto Sumeragi (皇 北都 Sumeragi Hokuto) is Subaru's twin sister who was killed by theSakurazukamori at the end of Tokyo Babylon. While she was still alive, Hokuto became friends with Kakyō after the dreamgazer drew her into his dreams. Being the first person he ever really met, she left a lasting impression on Kakyō. Hokuto is the reason he wants to die—so he can join her in the afterlife.
In the manga she appears in his reminiscence, while towards the end of the anime she actually appears to him as a ghost and persuades him to turn against Fūma in order to attempt to change the future. Kakyō enables her to cross into her brother's dreams, where she urges Subaru to rise from his catatonia and continue the fight, an important action that later buys Kamui enough time to understand what he should do.