Ability: Power to Reflect Sound Waves
You may have shouted "Yahooooo!" while climbing a mountain. If someone else shouts "Yahooooo!" in response, it must've been a Yamabiko.
She lives in mountains and when she hears a cheerful sound, she replies with a loud voice. A good youkai with a kind heart.
However, these days, superstitions like "Mountain echoes are only reflections of your sound waves returning you—" has become a common belief. Realizing the emptiness of paganism, she decided to become a Buddhist discipline.
Her ability works well with reciting Buddhist sutras. It is part of her daily routine while in the mountains.
Thus, she was recently known as "a sutra-reciting voice coming from a deserted mountain" and she was able to recollect her place as a youkai.