The Baron

Despite his tacky fashion choices, old age, and quirky personality where he wants everyone to be more "cheerful" and laugh at his jokes, the Baron is one of the most powerful characters in the series. His idea of making people "happy" is to turn them into one of his corpses, at which point he forces them to smile. As a minion of Aneyama, he is entrusted with the corpse of Nachi to do experiments on and to prepare for the fusion of the child of destruction with Riki-Oh. The Baron knows more than anyone besides Aneyama and Mukai, and while he is not seen having any contact with him it is quite likely that they have directly communicated at some point. He is the most essential minion in Mukai's plan and is easily more powerful than Aneyama, but the Baron's weakness to even remotely warm temperatures when he is otherwise invincible means Aneyama is presumably able to keep him under his thumb by keeping him contained within his laboratory.

The Baron has a laboratory full of corpses which he does his best to preserve in the best condition possible, whereas the alive villagers outside are treated lower than pig manure. The Baron has surgically attached the right hand of Nachi to his body, giving him the ability to heal anything he touches instantly and the ability to command the corpses. The Baron himself is already dead and needs none of his vital organs to function, demonstrated when both his heart and brain are removed at different points, though he is able to repair the damage with Nachi's hand anyway. He could presumably bring about the end of the world like Nachi could by touching his hand with Riki-Oh's, though he does not directly attempt this.

Perhaps even more powerful than Nachi's hand is the Baron's ability to remove and expand matter. Removing matter enables him to "teleport" himself or other people without even touching them, and he uses this ability to move Riki-Oh inside of a supposedly indestructible capsule with a quickly depleting air supply. He uses his ability to expand matter to extend his arm after Riki-Oh to try to hit him with Nachi's all powerful hand, and uses it to dislocate his head at will. Theoretically, the Baron could simply remove people from existence by removing matter, or expand the vital organs of an opponent to burst out of their body and kill them instantly. Presumably, he doesn't do this to Riki-Oh because he still needs his body. The Baron is easily the most intelligent character in the series and has invented laser swords that can cut through anything as a cliffnote, making Dr. Kohinata look like an amateur by comparison.

His only weakness is heat due to his undead status, so he fights inside of his lab kept at a cool temperature. He is so vulnerable to heat that just by being grabbed and restrained by Riki-Oh, he starts to melt due to his body heat. Even when reduced down to nothing but a skeleton, the Baron is still able to keep functioning, and claims that he is not defeated because he can clone himself. Of course, he is killed long before he can attempt to do that.

The Baron showcases Nachi's handBaron explains how he is able to remove matterThe Baron dislocates his headThe Baron expands matter to expand his armBaron uses Nachi's hand to heal himselfA skeletal Baron claims he will clone himself