Kokoro has sex with her master. (Pixiv Fanbox)

Kokoro is a maiko in Kyoto. Maiko are apprentice Geisha who entertain guests in Geisha parlours by performing traditional Japanese dances. Maiko need a patron, called a Danna-sama (master). Danna-sama support maiko (and later Geisha ) throughout their lives. Maiko (and later Geisha) pledge their life-long love to Danna-sama. It is not uncommon for Maiko to have sex with Danna-sama.