Dr. Kohinata

Dr. Kohinata (AKA Dr. Obinata) is the right hand man of Aneyama, who relies heavily on Kohinata's countless inventions to enforce his regime of brutality and cruelty. Dr. Kohinata created Evil-Oh, a physically enhanced clone who gave Riki-Oh a tough fight. He was able to control Evil-Oh with a violin of all things that he could hear from any distance somehow, as well as heal any damage he took. His other inventions include a mole man that can dig through the earth, a kitchen that could roast Riki-Oh alive, power armor to enable the frail 80 year-old Aneyama to fight Riki-Oh in hand to hand combat, and even a self destruct mechanism within Aneyama's palace that generated crystals that would supposedly bring about the end of the world. Kohinata also does regular transplants of Aneyama's vital organs to keep him alive in his old age, and is more likely than not the one who does his plastic surgery.

At some point in the past, Aneyama gave Kohinata a laboratory after he ran into a calamity involving misconducts with alcohol, women, and debt after he was kicked out of his university, with Aneyama giving him employment when he was desperate. Aneyama shows a large amount of trust in Kohinata and it seems to pay off to a degree, though when his inventions start failing he threatens to kill Kohinata if they don't start working properly. Kohinata shows massive loyalty to Aneyama, possibly just out of fear, but he is willing to start "plan C" on Aneyama's command, which brings about the end of the world.

It is easily within Kohinata's power to betray Aneyama given he outright does a heart transplant on him and creates power armor for him to wear. With the creation of Evil-Oh, Kohinata proves he could even create a sock puppet clone of him to do whatever he says so he wouldn't even have to deal with the aftermath of the event from other characters such as Mukai. The fact he doesn't is a rather large display of his loyalty despite how badly Aneyama can treat him at times. Given Aneyama is confirmed to be over 80 and Kohinata also looks fairly old, it is likely they have known each other for a significant portion of their lives based off the fact Aneyama recruited Kohinata while he was still in university.

Riki-Oh does not take Kohinata at all seriously at first despite his competence, presumably due to the fact that he does not fight directly. Riki-Oh says that "somebody like him isn't worth killing" in their first encounter, only for Kohinata to get the slip on him and to lure him into a trap that ultimately leads to the events that get him defeated. Kohinata has a grudge against Riki-Oh for not being taken seriously, as when he is weakened and vulnerable he slashes Riki-Oh several times in anger, taking out his pent up frustrations on him. In chapter 62, Riki-Oh says that he could "never forgive these bastards" in reference to Aneyama and Kohinata, showing that he now takes him seriously, but Nachi insists that Riki-Oh must forgive the villains. Aneyama continues trying to kill him and eventually dies for it, but Kohinata takes advantage of this and flees, being one of the few major villains to survive the series.

The violin used to control Evil-OhKohinata's past with AneyamaKohinata gets revenge on simpleton Riki-Oh