Dianyan is a pure diamond Yo-kai with big black eyes. Its muzzle and paw tips are solid white, while its inner-ear and nose are gold. Around its belly is a pure gold band to match it's collar, which has an ice blue sphere hanging from it. It has bright yellow tail-flames
He tends to look down on other people without meaning to, which causes him to have no friends. He also likes to keep whatever he finds, even if it's not his.
His diamond paws can crush mountains according to him. Also, by rolling around, his diamond body can destroy anything.
Dianyan debuts in a brief appearance in Yo-kai Top Ten, claiming the #1 spot in a Yo-kai Top 10 countdown of the most popular Yo-kai despite not having made any appearances in the series up to that point.
Dianyan later appeared in Yo-kai Gojidatsujii, where he and all the other cat Yo-kai were summoned all together due to Gojidatsujii's power changed the Robonyan F's Dream medal's name to 'Nyan'. Unfortunately, shortly after Gojidatsujii ran away for his life, Nate accidentally said that he summoned all of them for nothing, thus unintentionally upsets the cat Yo-kai and this led to them proceed to beat up Nate and Whisper while welding shinai (a type of bamboo-made katana made for practicing kendo.) as the episode ends.