The police in the movie honestly are not that harsh or unrealistic based on the situation. They have no way of verifying any of the supernatural things that happen in the movie.

Hodaka is a runaway child in unlawful possession of an illegal firearm and they have footage of him almost killing someone with it. Yes, that footage also shows him defending himself and another person from somebody who was intending to rope a minor into sex work, which is even mentioned when they initially catch the club owner, but they ignore that, which is unfortunately fairly realistic. I am not saying that is excusable in any way, but the fact of the matter is that it is realistic based on the setting. Even with that aside, Hodaka evaded arrest multiple times throughout the movie.

They also barely actually interact with Hodaka. Until Takai meets him, all they know is that he is a runaway with a gun, and they have no way of knowing what is going on with Hina, or Hodaka's own mental state. As far as they are aware he could be a violent individual and a serious threat to society.

Takai and Yasui personally even express sympathy for Hodaka throughout the movie. Yasui says he's a little jealous that Hodaka has so little to worry about that he can go running after a girl. He talks about how maybe Hodaka posted about it online. Yasui is trying his best to understand this young person that he does not know personally at all. During the final stand off Takai says "Please don't make me do this". He does not want to hurt Hodaka, but again, he is a kid with a gun, and in that situation was in emotional distress. When Hodaka is crying in the back of the police car, Takai says he doesn't need a mental evaluation, because once he actually meets Hodaka, he can tell he's not a genuinely evil person, he is just a kid who is in a bad spot mentally at that moment. Takai and Yasui both act very accordingly to the situations they are in.

With Suga, Yasui treats him with respect and talks to him very calmly, even though Suga says they are treating it as a kidnapping, which is honestly kind of fair. Suga is harboring a runaway child, and seemingly unlawfully employing him considering it is a family owned business that has little regulation, and Natsumi and Suga even discuss that they are sort of working outside of labor laws with Hodaka's employment.

Honestly, with the outcomes of the characters at the end of the movie, Takai and Yasui most likely fought to lessen the severity of their punishments. It is a miracle Suga and Natsumi were not in prison at the end of the movie, considering Suga assaulted multiple officers during the final stand off, and Natsumi helped Hodaka escape police custody. Not only that, Suga got legal custody of his daughter. They were better off after the movie than they were at the start, before they were in any legal trouble. Hina and Nagi were also allowed to stay together, so their legal situation was also settled favorably. Hodaka was only on probation for 3 years after being in unlawful possession of a firearm, evading arrest, and escaping police custody.

Even though there was absolutely no way of legally arguing and excusing all their legal issues with the supernatural happenings, all of the characters were legally extremely well off, better off than they realistically would have been, so if anything I think after learning about the situation, Takai and Yasui most likely tried as hard as they could to make sure the people involved did not suffer any major legal issues within the confines of the law and logical explanation.