Kikai Banashi Hanasaka Ikkyuu

There once was a monster called Karma who loved to challenge his victims to a battle of wits. If the subject succeeded, the monster would grant them one wish, but if they lost, he would devour their soul. At the same time, there was a young monk called Hanasaku Ikkyuu, who was famed for his cleverness. He used to eagerly sharpen his mind, solving challenging riddles sent to him, until his mother fell ill. When he found that his cleverness was of no use in helping her, he gave it up.

Karma seeks out Ikkyuu, eager to bet him in a battle of wits and consume his soul. One day, Ikkyuu rescued a young beggar boy, only to see him fall ill with a mysterious illness. That same day, Karma finally finds Ikkyuu and offers him his dangerous bargain. Thanks to Karma, will Ikkyuu finally have a way to use his cleverness to help the people around him?

(Source: MangaHelpers)