Yoon Dan-ah from Yo-kai Watch Shadowside. A 14-year-old middle school girl with a righteous heart and a lively personality who helps Yo-kai and friends in crisis. She is warm-hearted and kind, but bold enough to speak up against injustice. One day on her way home, she meets Whisper and unexpectedly becomes the owner of the Yo-kai Watch Elder. After hearing the explanation from Yu-seong's grandmother, Cheon Yu-seong, and Whisper, she agrees to cooperate to defeat Rasen. She is a childhood friend of Seo Do-young; they were close in elementary school but grew apart in middle school, only to reunite now. She seems to have feelings for Do-young.

Seo Do-young from Yo-kai Watch Shadowside. A 14-year-old handsome middle school boy. Since both his parents are researchers, they were often away for work, leaving him alone even on his birthdays. This caused him to close off his heart, distance himself from others, and develop a lonely, dark personality. However, he is fundamentally kind and gentle, possessing a pure, 'cool' personality that treasures friends. Unlike other victims infected by the Onimaro, he maintains his appearance and reason, controlling the power to punish a trio of bullies. Deceived by a one-eyed ghost in a black robe who promised to remove all evil-doers and show his existence to the world, he began controlling Onimaro as a servant of the Oni King. However, he refuses to attack Dan-ah's group when they find him. He currently uses the Kigan Gear, but if he clears up the misunderstanding about his parents and becomes an ally to Dan-ah and Yu-seong, he will become the owner of the Yo-kai Watch Ogre. He is Dan-ah's childhood friend; they were close before he closed his heart. He seems to like Dan-ah quite a bit.

A 14-year-old middle school boy who can see Yo-kai, perhaps because he comes from a family of exorcists. He is a comic relief character—active, positive, and incredibly generous. As a member of an exorcist clan, he hears about the Onimaro and the Yo-kai Watch from his grandmother and struggles to stop the virus.

Whisper from Yo-kai Watch Shadowside. A butler Yo-kai who sometimes acts a bit foolish and always carries a Yo-kai Pad. He uses the pad to explain the names and characteristics of Yo-kai. A comic relief character.

A giant the size of a building. His goal is to destroy and vanish the world that has been polluted by interference, exterminate humanity, and recreate a new world ruled by Yo-kai, free from human meddling. He spreads Onimaro and can strengthen himself by absorbing the Onimaro he has scattered.

Jibanyan from Yo-kai Watch Shadowside. A red cat Yo-kai. He is strong enough to crush cars. His Lightside form is quite cute, a two-headed tall figure standing on two legs. His Shadowside form is a massive body surpassing an adult male. He uses the 'Hundred Paw Strike.' He is a tsundere and sharp-tongued. He is fanatically obsessed with chocolate bars.

Though they look like small, cute ogres, they are a Yo-kai virus that spreads a human virus, multiplying through human evil and driving humans and Yo-kai to the brink of extinction. Once they start multiplying, it is eventually impossible to stop them. Infected humans turn into hideous ogres, amplifying their malice until death and forcing them to commit sins. They are two-headed tall figures. Their numbers increase by possessing dark emotions like loneliness, jealousy, and anger. They are invisible to ordinary people.

A trio of Onimaro who first possessed Do-young. Wang-nun is the leader, the most active and lively of the three, and has one eye. Du-nun is a relatively calm and cautious two-eyed Onimaro. Sam-nun is an innocent three-eyed Onimaro with a habit of saying 'Yay~'. They eventually develop sympathy or affection for Do-young; if he is in danger of being disposed of, they will try to protect him, be branded as traitors, and become the only Onimaro not absorbed by Rasen. Wang-nun, Du-nun, and Sam-nun are good-hearted.

A male snake Yo-kai. In Lightside, he is a muscular one-eyed Yo-kai with purple skin, wearing black gloves, boots, and shoulder guards, dressed like a tokusatsu hero. However, his true form in Shadowside is Mitsumata Nozuchi (Slimamander), a boss Yo-kai from the classic series. His special move is the 'Samsik-i Beam,' a petrification ray from his eyes. He vows to protect Dan-ah. He is surprisingly cowardly and a bit of a klutz. He serves as a main comic element, often paired with Whisper and getting scolded. He is an ally to Dan-ah's group.

A white dog Yo-kai. He retains his habits from when he was a dog before dying. In Lightside, he looks like an ordinary dog, but in Shadowside, he transforms into a creature resembling a Haetae. In Lightside, he is calm, rational, and gentle. He is an ally to Dan-ah's group.