Osore (畏, Fear) is the term that denotes the unique skills and traits of each yōkai. It refers to the "fear" of the unknown, an emotional reaction produced when the yōkai represent themselves as "monsters". As yōkai first existed as creatures who induce fear in humankind, the general concept of "fear" revolves around being feared and respected by humans and making them feel small and weak. It involves exerting a wall of pressure to make one's presence feel larger than the actuality. When done correctly, this also creates a change in the mood and surrounding air - as seen whenever a dense fog appears when a Hyakki Yakō gathers in the series. Itaku states that Osore only applies to scaring humans.
A yōkai's "fear system" determines the sort of skills they use and their area of specialty. A fear system is a reflection of the yōkai species that performs it, and can often aid in identifying unknown yōkai. It also isn't too uncommon for a yōkai to combine two types of fear systems to achieve a desired effect (such as Muchi's combination of wind and poison).
Elemental-based fear systems make use of natural elements like water, wind and fire. Yōkai with an elemental-based fear system are strongest when fighting in their particular element and can, to varying degrees, use their fear to manipulate naturally-occurring instances of their element.
- Water: Yōkai who specialize in water-based fear are often water-dwellers themselves. They are able to manipulate nearby water and use it to strengthen their own techniques and can remain underwater far longer than other species. In the absence of water, they can become considerably weaker and some are even forced to rely on natural occurrences due to an inability to produce water on their own.
Users: Kappa, Gangi Kozō, Amezō
- Fire: Fire-based fear users are able to withstand and survive in intense heat and may even be able to produce fire inside their bodies. They are able to direct the path of nearby fire to suit their needs. Though they are strong in the presence of fire, they can be overpowered by a flame which has been combined with a stronger fear.
- Ice: Ice-based fear users thrive in cold environments and often give off a chill from their bodies and mouths. Though they may not be able to manipulate natural instances of ice, they can produce their own. Despite being considerably weaker in the presence of heat (including hot water), they can use their fear to regulate their own body temperature in order to withstand it.
Users: Tsurara, Setsura, Reira
- Wind: Wind-based fear users are able to create winds of varying severity out of nothing. Their very presence seems to stir the air itself and many are also capable of flight as a result.
Users: Itaku, Muchi, Kuroumaru, Sasami, Tosakamaru, Akujo Nokaze
- Darkness: Darkness-based fear users can shroud an area in blackness and, by extension, greatly reduce visibility for those affected. Users themselves have no difficulty seeing in complete darkness and are often adept at moving silently to take advantage of that strength.
- Poison: Poison-based fear users are able to stun or immobilize those who attack them, and can often produce poison within their bodies. They tend to have a high resistance to poisons and ailments originating from outside sources, and some can even sense the presence of poisons caused by other yōkai.
Users: Zen, Muchi
Physical-based fear systems rely on boosting the user's strength to bodily overpower and/or overwhelm an opponent. Users are often strong even without activating their fear, and are capable of withstanding far more damage than other yōkai.
Users: Aotabō, Hihi, Shōei, Tearai Oni, Raiden, Gairōta, Gaijirō, Gaitarō, Kyūso, Hakuzōzu, Tsuchigumo
Manipulation-based fear systems come in two varieties: the sort whereby the user manipulates others and the sort whereby the user manipulates themself. Those who manipulate others are able to direct a target's movement and actions, often through the use of marionette-type thread or spoken suggestion. Those who manipulate themselves can alter their own bodies to use as weapons. Some can even go so far as to alter the shape and/or appearance of their own body so as to resemble someone or something else.
Users: Mezumaru, Gozumaru, Hari Onna, Kejōrō, Tamasaburō, Hebidayu, Enchō, Mamedanuki, Satori
Displacement-based fear users are adept at making themselves difficult to locate and, by extension, attack. Users are strongest against opponents who rely heavily on sight and considerably weaker against opponents with natural reflexes. They can often mask their own fear, making themselves as easy to overlook as part of the scenery.
Users: Nurarihyon, Rihan Nura, Rikuo Nura
Creation-based fear users often don't exude much fear themselves, but are able to produce yōkai or other creatures which do. Users are strongly reliant on being able to create, and are able to bring to life whatever they have drawn/written. Some may even be capable of altering other living beings into one of their creations, by using them as a base.
Presence-based fear users are able to overwhelm an opponent through the sheer immensity of their fear alone. It could be said that theirs is a fear which causes fear, and users often make use of a secondary fear to take advantage of an opponent's hesitation in the face of their "presence". Users are frequently either physically huge/grotesque or associated with much older folklore and the strength of their fear is in part due to their legends.
Users: Gyūki, Great Tengu of Mount Kurama, Inugamigyōbu Danuki, Hagoromo Gitsune
Weapon-reliant fear users tend to channel their fear exclusively into a weapon with which they have superhuman proficiency. Users are rarely seen without their signature weapon, but are able to alter its shape, size and density as the situation requires. Weapon-centered fear may even make use of items that would not normally be considered weaponry, such as string.
Belief-reliant fear users come in two varieties: battle-oriented and non-battle oriented. Battle-oriented belief users become stronger the more human belief they possess, and often feed off humans' fear in order to maintain that strength. Some are even capable of stealing belief from other yōkai. Non-battle oriented users require human belief and/or prayer in order to maintain their own existences. Often, in order to use their abilities at all, they must possess a certain level of human belief.
Users: Senba, Kokehime, Sodemogi-sama, Nijūnanamen Senju Mukade
Grudge-reliant fear users are often created as a result of someone or something's grudge. Users thrive on hatred, and grow stronger the more hatred they feel toward an intended target. They become considerably weaker if they are deprived of the backing for their grudge but, over time, a grudge-reliant fear can evolve into presence-based fear, as evidenced by Gyūki.