Kosei Yamanouchi was a famous mystery writer who left a huge legacy and died suddenly before the age of 60. In the original and the anime, he was a tired old man who looked like he was going to die at any moment, but in the drama, he is a nice middle-aged man who seems to be full of energy.
His representative work is "Russia Doll Murder Case". He is a top-notch full-fledged mystery writer who has been highly evaluated by mystery fans for his series of bizarre tricks. During his lifetime, he was touted as a person of character and was very popular, and he formed an amateur orchestra with five acquaintances and provided financial support.
He selects the five people as inheritance candidates and leaves behind a legacy scramble code game to find out the whereabouts of the will. However, in a video letter that gathers all the game participants and publishes it, they reveal the "secret of money troubles" of the five people to arouse suspicion, and the peephole in the room leads to Kirie's room. And the insidious nature that was hidden during life is gradually revealed.
A person who can't read his true feelings to the extent that Yugetsu also looks at him with suspicion, saying, "I hated him so much that I wanted to kill him."