These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
First is the prison doctor Sasaki. Sasaki hides behind the veneer of a kindly old man but in reality, he is a cruel sadist who regularly rapes attractive male prisoners. Sasaki coerces them by holding privileges and favors over their heads. One prisoner is eventually Driven to Suicide thanks to Sasaki's molestations. Sasaki schemes with the warden Ishihara to murder anyone who knows the truth and after leaving behind the prison, continues molesting young boys when conducting a political campaign.
Sasaki's partner in crime at the prison, Warden Ishihara. Ishihara is a corrupt prison warden who delights in exercising sadistic authority over the prisoners by regularly conducting beatings or giving out punishments that are massively out of proportion to minor offenses. Ishihara gives prisoners to Sasaki to rape and proposes murdering those who discover the truth to cover his tracks. When the series' initial hero, Sakuragi, finally defeats Ishihara, he gives the warden the evidence of Sasaki's crimes to make Ishihara leave his friends alone. Ishihara's response is to stab him.
Fridge Logic: How did Yokoyama know Mario wanted to be a boxer and thus smash his hand? Mario had barely even begun to consider boxing as a future career/dream, it wouldn't exactly be common knowledge.