Nobiagari is a yokai that appears out of nowhere and quickly swells to massive size. Often stalking its victims from behind and thus just out of clear sight, the details of its origin and physical appearance differ greatly from region to region. Some describe it as an ethereal living shadow; other as a humanlike creature, somethimes in the guise of a Buddhist monk; and still others say that it is some sort of animal that has gained the ability to trick humans into believing that it is far larger than it actually is. Whatever the case, the Nobiagari's true form is believed to be that of a strangely proportioned humanoid - perhaps inspired by the strange shapes our shadows cast on the ground late in the day - that leaps into existence gives chase to startled travellers. They are said to appear more frequently on paths near water, particulary lakes and rivers.
If it truly is a shadow, the Nobiagari is essentially a personification of the sundial effect. According to these legends, the Nobiagari can potentially show up any time the sun is low in the sky - essentially, just before twilight, the traditional time at which yokai tend to appear. However, logic dictates that encounters are probably more common in the winter months, when the days are short and the sun is low in the sky.
The Nobiagari shares its modus operandi with a veriety of similar yokai, most closely that of the Mikoshi-Nyudo (the "Look-up Monk"). The Mikoshi-Nyudo takes the form of a Buddhist monk who appears suddenly before travellers on deserted paths or streets, growing to immense proportions as the viewer looks upon him. Like the Nobiagari, the Mikoshi-Nyudo may be the handiwork of a smaller animal; the people of Hinoemata village in Fukushima Prefecture believed the perpetrator to be an itachi, or Japanese weasel, though the actual relationship remains unconfirmed. Local legend has it that shouting "Miokoshitari!" ("I can see over you!") at the yokai drives it away.
Other relatives include the Shidaidaka of southwestern Japan; the Takanyudo of Shikoku Island; and the Norikoshi-Nyudo of Iwate Prefecture in northern Japan. Although the specific Habitats, initial appearances, and maximum sizes of these yokai differ from locale to locale, their characteristics and patterns are extremaly similar. It remains unknown whether these variations represent different "species", or multiple appearances of the same yokai embellished with local favor.
- Nobiagari in Yokai Attack!: The Japanese Monster Survival Guide