But then we have another plot hole. There wasn't any time for police to even notice any criminal activity from him! The accusations were apocryphal and literally fell out of the sky. Reading the damn thing, the absolute bare minimum of justification necessary for the cops to go after him, would take at least a few minutes. Then you would have to contact HQ and obtain a warrant to do ANY monitoring, that would be a few more minutes. That's enough time to get away from the crowd, taxi his way home and pack up his crap (and some food!) to leave the city!
The story was sold to the Nittei Shinbun, who's supporting his opponent, with the opponent being the son of the current governor of Tokyo, the day before the papers were released.
The paper took the time to print for next day publication, with the reporter who was close enough to the governor of Tokyo to play mahjong with him. And from the looks of things, the articles were scattered midday when Makoto was giving his speech.
So before 3pm the previous day (so the printers would have time) they sold the story, then close to noon the next day when the articles were released during the press conference. Especially with the governor of the city that they are literally in is involved, that's more than enough time to setup investigations and round up his associates first before going after Myanouchi.
You mention him getting away from the crowd and taxiing home before leave the city, how? His home would be the first place the police would go, to secure evidence. He might as well present himself to the Tokyo PD HQ.
And if he left, where the fuck would he go? He's a politician running for office in Tokyo. All his networking, assets, contacts etc would be in Tokyo. Hell the police and banks would put a freeze on his accounts and anything related.
His campaign pushed him using social media and legacy media, his face is known across the net and tv/print.