Yahiko first appeared as a white fox with closed eyes and a large fluffy tail that eventually splits into three. His ears and front paws has black fur, around his neck a yellow cloud-like scarf.
In his human form, he takes on the form of a young boy around the age of 12. In this form, he has short light brown hair and dons a white and reddish-brown kimono and sandals. He is usually seen with a smile. However, when he is angry or serious, his eyes are narrowed and turn red.
Yahiko acts like a child, he wishes to play with everyone as long as he wants. He always is quite mischievous as he secretly ate food from Zenko's temple. He also likes to be brushed by Zenko. He is also scared that the people he knew will change, as seen when he said to Haruitsuki that he heard nasty rumors and was happy that Haruitsuki is still the same, though a bit scarier.
Yahiko is able to transform into a fox or human at anytime he wants to. Unlike other yōkai, Yahiko's transformation ability is shown to extend to inanimate objects, as shown when he transformed into a gravestone while playing Hide-and-Seek with Haruitsuki, Hanae and Zenko in Chapter 15. It has also been shown that Yahiko can transform in another person's appearance, as shown when he transformed into Haruitsuki in the same chapter, or to any physical appearance imaginable as shown when he was playing Hide-and-Seek with Haruitsuki and Hanae as part of Hanae's yōkai-sensing training.
Yahiko is able to fly in his fox form.
Yahiko is able to give seals by biting people as shown in Chapter 14.
Yahiko has a threatening aura but is capable of concealing it to the point Abeno couldn't detect him when they remet after eight years.
Yahiko met Haruitsuki when he was seven, lost in a forest and ended up playing hide and seek with Haruitsuki for three days. Eventually, Yahiko heard nasty rumors spread by other yōkai and was worried that the Haruitsuki he knew was no more. After reuniting with Haruitsuki, he was a little disappointed that Haruitsuki was unable to recognize him. Eventually, Haruitsuki remembered Yahiko and forced him to apologize to Zenko for biting and putting a seal on her. Yahiko commmented that Haruitsuki has become scarier than before. Yahiko only likes to be carried by Haruitsuki and enjoys being with Haruitsuki.
Haruitsuki is also shown to care about Yahiko a lot even though he refers to Yahiko as a three year old kid. When Hanae's influence nearly hurt Yahiko, Haruitsuki intervened just in time to kick Hanae out of the way to rescue Yahiko.
Yahiko met Hanae, he forced him to play hide and seek, along with Haruitsuki and Zenko, in exhange for the removal of the seal on Zenko's wrist. Yahiko is not that fond of Hanae but they are on friendly terms. He volunteered to train Hanae's yōkai detecting skills by playing hide-and-seek with him during the photography overnight trip by which he scares Hanae a lot with his 'free add-ons' while playing.
He is the second victim to Hanae's influence.
Yahiko met Zenko and bit her in order to force Hanae and Haruitsuki into playing hide and seek with him. He wanted to play with them immediately but was stopped by Zenko, saying that they have class. They ended up playing hide and seek at a graveyard near Zenko's temple. After Haruitsuki forced Yahiko into apologizing to Zenko for putting a seal on her, Zenko said that as punishment, Yahiko will have to help out at her temple. Yahiko likes it when Zenko brushes his fur in his fox form. Yahiko is fond of Zenko.
Yahiko first meets Kinako in a forest with Okina. Yahiko was in his fox yokai form and scares Kinako saying "Found you" while she was eating leaves. Kinako fainted thinking that Yahiko was going to eat her.
After that, Yahiko and Kinako became friends. Yahiko became Kinako's favorite playmate and she enjoys playing hide-and-seek and tag with him. When Yahiko transformed to his other form, Kinako didn't recognise him. But when Kinako tranformed, she obtains just the ears which looks similar to that of Yahiko. In the process she loses energy, worrying Yahiko greatly.
Yahiko cares a lot for Kinako, so he forced Haruitsuki to exorcise her. Yahiko and Kinako played together one last time before Kinako was exorcised. Yahiko was sad to let her go but assures himself that it is the right thing to do for her well-being.
- Like many yōkai, Yahiko's sense of time differs from human sense as they live long lives.
- Yahiko's likes include snacks (especially rakugan), hide-and-seek, and Haruitsuki while he dislikes Hanae.