Yo-kai in the franchise are based on yōkai, supernatural creatures and phenomena from Japanese folklore.
The word yōkai is a broad Japanese term for mysterious beings, spirits, monsters, and uncanny occurrences. Traditional examples include shapeshifting animals, river creatures, household spirits, and beings associated with particular places or fears. Yo-kai Watch adapts that enormous folklore tradition into a collectible cast with distinctive personalities, designs, powers, and social roles.
The games do not treat every Yo-kai as simply an evil monster. Many are mischievous or troublesome, while others are helpful, lonely, comic, or misunderstood. The player’s goal is often to discover why a person is behaving strangely, identify the responsible Yo-kai, and either resolve the problem or befriend the creature. This approach gives the series a lighter tone than many traditional ghost stories.
Tengu, oni, and kami are all genuine categories or figures associated with Japanese religion and folklore, but they are not the overarching answer. They are narrower examples or related concepts. Yōkai is the broad source tradition that supplies the franchise’s creatures, even though the games freely remix older legends with original characters such as Jibanyan and Whisper.