Shiki eventually learns from diaries that Hisui and Kohaku were taken in by Makihisa Tohno to serve him as Synchronizers, to supply him with energy to suppress his demonic blood. Kohaku in particular was raped and never allowed to leave his side. Hisui was unharmed on Kohaku's behest, as she took in all the abuse to keep her sister away from Makihisa. Akiha and Hisui eventually discovered this, and managed to end the abuse. With Shiki's departure, Hisui degraded in emotion, becoming trapped in her sadness and longing; this, in turn, causes Kohaku to suggest their trading of places. As time went on, the one with the heart of a girl gained the skin of a doll, an indifferent face hiding a wealth of feelings; and one smiled in all situations, a doll's heart masked by a girl's skin.