Woodpecker Detective's Office (Kitsutsuki Tantei-dokoro)
Title: Woodpecker Detective's Office (啄木鳥探偵處, Kitsutsuki Tantei-dokoro)
Manga: Not that I know of
Publisher: Tokyo Sogensha
Description: It is the end of the Meiji Era. The genius poet Ishikawa Takuboku, who’s struggling financially, starts a detective business out of his lodging in response to a certain murder case. He calls it the Woodpecker Detective’s Office. "The ghosts of the Twelve-Story Tower in Asakusa," "the man-eating figure who wanders the streets on snowy nights"... Takuboku involves himself in one bizarre case after another with his hometown acquaintance, Kindaichi Kyosuke, as his assistant. (Copied from Crunchyroll)
This is probably a long shot as it’s not a light novel but a regular mystery novel, but it recently had an anime adaption which I really enjoyed. The premise is famous Japanese authors solving mysteries. The character names should be familiar from Bungo Stray Dogs or Bungo to Alchemist, but it’s not supernatural or fantasy.