Ichiko, a black-haired Zashiki-warashi spirit and one of twins, was discovered by Hozuki in an abandoned human house before relocating to the Hell Palace. Originally nameless, the twins had remained invisible to humans and communicated solely with each other using generic terms. Their move to Hell exposed them to beings who could perceive and interact with them, motivating a request for distinct names. During the naming process, Hozuki and Momotaro referenced traditional Japanese conventions, observing that numerical names like Ichiro or Jiro were typically male-oriented and uncommon for girls. Hozuki assigned "Ichiko" to the black-haired twin due to her consistent role in initiating conversations and leading interactions, while her sister received "Niko." Their integration into Hell featured an episode where Hozuki experimented to verify the Zashiki-warashi folklore trait of bringing prosperity to inhabited households and misfortune upon departure.