Name an anime character that's completely evil

THE MAJOR - HELLSING
The Major is a Nazi, which is really all needs to be said. Nazis are the worst. However, the Major is evil even among Nazis, mainly because he’s really, really prepared. After fleeing Germany at the end of World War II, the Major planned for 50 years to take his revenge on England, amassing an army of vampires, monsters, war-zeppelins, and more. Not only is he good at war, he really, really enjoys it — his plan wasn’t just to begin a new 1,00-year Reich, his plan was to so fuck up the world that he could stay at war the entire time, too. He killed three million people, pretty much for kicks, and destroyed Alucard in a trick that involved him sucking up all the blood in the annihilated London. That’s… that’s pretty impressive. And evil.

Johan Liebert from Monster
Known for bringing out the worst in people just through words alone. Without spoiling too much, his actions include...
-Causing orphans and the guards of the orphanage to murder each other as he watched
-Murdering all of his previous foster parents using hired killers
-Driving a detective to suicide
-Causing multiple children to play a suicide game, resulting in several of their deaths
-Drives a child to attempting suicide by both telling him his mother never wanted him and showing him the human atrocities taking place in the Red Light District, like drug abuse and rape
-And turned a small, peaceful town into a warzone, with hundreds killing each other, to find one man.
And that's just the major ones. There's many minor things he did that were pretty awful. He also finds no enjoyment in anything. It's a small detail, but it's VERY important

Shou Tucker from Fullmetal Alchemist.

The perfect example of how being obliviously evil isn't always a "Get out of jail free" card, it actually makes him worse.

Kiruin Ragyo

Frieza, Cell, Majin Buu (before he absorbed the Kais), Cooler, Broly, Janemba, Hirrudegarn, Hatchiyack, Baby, and Omega Shenron from DBZ and GT.

naraku from inuyasha
Naraku was consistently portrayed as incredibly cruel and manipulative, using others to satisfy his own interests and taking great sadistic delight in destroying the bonds and lives of others.Above all else, Naraku was power-hungry and self-obsessed, desiring only power and sheer dominance over others. He bore nothing but contempt and disgust towards all other beings and considered himself superior in every aspect

and also rido kuran from vampire knight
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Rido was a very entitled character who takes pleasure in antagonizing others. He believes in indulging his desires and to have power is to crave for more and there is nothing wrong in simply taking more power. Lascivious, self-centered and cruel, Rido is powerful and not hesitant to use that for his own gain and the destruction of others.

Medusa Gorgon from Soul Eater !!!!

Griffith from Berserk.

Rido Kuran-Vampire Knight (He killed his own brother.)
Tucker-FMA (For alchemy's sake !!!!!He turned his daughter into a chimera!!!!)
Chimera: something thats turned Half human half animal with alchemy.

Shishio Makoto from Rurouni Kenshin

He's ruthless, coldblooded and sadistic. He manipulates and uses everyone, believing "the weak exist for the benefit of the strong". He almost succeeds in his plans to take down the Meiji government and actually beats the protagonist Kenshin in their fight. The only reason he dies is because he willingly allows his body to spontaneously combust, his final words being that he's going take over hell.

Frieza (Dragon Ball)
Akainu (One Piece)
Acnologia (Fairy Tail)
Father (Fullmetal Alchemist and Fullmetal Alchemist Brotherhood)
Dark Marik (Yu-Gi-Oh!)
Grings Kodai, Hunter J, Dr. Yung, and Jarvis (Pokemon)
Nightmare (Kirby: Right Back at Ya!)