|First Appearance||Episode 1|
Mitsuo was part of the investigation squad in charge of discovering who destroyed Norihiko Yokoya's MLM. When he was about to reveal what actually happened, Akiyama Shinichi's mother committed suicide, making it very unlikely that she was responsible. Mitsuo had discovered that she was, but his employer would not believe him. This led to a brawl between the two, causing Mitsuo to have to take up a new job as a policeman.
Liar Game, Round 1Edit
Tanimura was on duty when Kanzaki Nao turned in ¥100 that she had found. There were multiple cases like this before, so he informed her that the owner would certainly be happy. He knew by this point that she was to be selected for the Liar's Game, so it came as no surprise when she came in the next day with ¥100,000,000. He told her that the police force could not do anything about money that was hers, and that she would need to hold on to it. He talked with her for a bit, and then said that she might want to enlist the help of a swindler. Akiyama Shinichi just got out of jail, so she went off to find him. This was part of Mitsuo's plan, as he said he would help Yokoya out in his revenge by ensuring that Akiyama made it to the Liar's Game.
Once the first round had ended, Tanimura made sure to see Nao again and tell her that if she just told the LGT to leave her alone, they would. It helped that he was an officer, so he came along with her... or so she thought. It turns out that he simply drove her there and ditched her, forcing her to enter the second round.