Jikininki, the corpse-eater
A shapeless thing comes in the night and eats a corpse and its offerings, while Musō, keeping watch beside them, can neither move nor speak.
Zack Davisson's 2015 retelling on yokai.com names the monk Musō Kokushi and starts the story earlier. On a pilgrimage, Musō lost his way in the mountains and came at dusk to a run-down hermitage, where an old monk pointed him to a village close by. He got there just as night fell.
In Wikipedia's summary of the tale, once a young man and the other villagers have left, Musō kneels beside the body and the offerings and begins the service. In the darkest hours of the night a shapeless being comes in while he is deep in meditation. He can neither move nor speak as it eats the corpse and the offerings.
Hearn's own telling in Kwaidan dwells on the eating. The Shape, as Hearn calls it, picks the body up as if it had hands and eats it faster than a cat eats a rat. It starts at the head and leaves nothing, hair, bones and shroud included. Then it eats the offerings and goes.
Next morning the villagers come back and Musō tells the young man what he saw. According to Wikipedia, the young man was not surprised.
"He saw that Shape lift the corpse, as with hands, devour it, more quickly than a cat devours a rat,—beginning at the head, and eating everything: the hair and the bones and even the shroud. And the monstrous Thing, having thus consumed the body, turned to the offerings, and ate them also. Then it went away, as mysteriously as it had come."