A spirit speaks through a medium to reveal how he died and the lies in the other character's testimonies in his most famous story.
In one work by this author, the realization that he can compose the perfect funeral dirge causes Krabach to leave jubilantly from the scene of another character's suicide; later in that work by this author, a group of 17 people hold an interview with the soul of that deceased poet Tok. The protagonist of that novella by this author falls down a hole after chasing Bag the fisherman, one of the title creatures, and Patient 23 relates his life among those creatures from an asylum. In addition to Kappa, this author wrote about a character who learns of the death of his brother-in-law, who was hit by a train, while copying the phrase "all right" over and over; that character anguishes over going to a psychiatric hospital, equating it with death, though he is haunted by hallucinations of "Cogwheels". A spirit speaks through a medium to reveal how he died and the lies in the other character's testimonies in his most famous story. For 10 points, name this author of "In a Grove", which was adapted into the film Rashomon by Akira Kurosawa. 
In one work by this author, the realization that he can compose the perfect funeral dirge causes Krabach to leave jubilantly from the scene of another character's suicide; later in that work by this author, a group of 17 people hold an interview with the soul of that deceased poet Tok.
Akutagawa Ryunosuke [prompt on "Ryunosuke"]