OVA
Description
Niko is one of twin Zashiki-warashi spirits adopted by Hozuki following their encounter during his haunted house tour in the human world. Originally haunting an abandoned house, the twins amused themselves by playing pranks on visitors, such as mysteriously appearing in photographs. This mischief drew Hozuki's attention, prompting him to test their luck-bringing abilities at Hakutaku's residence before formally inviting them to reside in Hell Palace.

Before adoption, the twins existed without individual names, their invisibility to humans and exclusive interaction with each other rendering names unnecessary. Their relocation to Hell, where inhabitants could perceive and interact with them, sparked a desire for distinct identities. Hozuki named the white-haired twin "Niko," applying a birth-order convention typically used for boys (akin to "Jiro" for a second son), while her black-haired sister received the name "Ichiko." This naming reflected their established dynamic, where Ichiko often initiated conversations and Niko followed.

As a Zashiki-warashi, Niko embodies the traditional folklore traits of these household spirits. Originating primarily from Iwate Prefecture, such spirits manifest as childlike figures aged five or six, believed to bestow fortune on diligent households but depart if residents grow complacent. Niko and her sister align with this depiction, appearing as young girls capable of influencing prosperity. Their supernatural nature includes invisibility to ordinary humans and a propensity for mischief, though within Hell, their presence serves bureaucratic purposes rather than domestic luck.

Integrated into Hell's administrative structure, Niko and Ichiko participate in daily operations. Their playful pranks coexist alongside official roles within the environment of organized punishment and celestial bureaucracy, contributing to the atmosphere through lighthearted antics. Their adoption underscores Hozuki's unexpected fondness for managing unconventional beings, placing them within Hell's broader mythological ecosystem.