It's kind of iffy if he can be considered a villain of just another victim, but Jinno/Kuma from
Afro Samurai is definitely a character I can feel sympathy for. Jinno saw his entire life fall apart and the people he considered to be his family die in front of him just so Afro, a person he considered to be his brother and closest friend, could get just one step closer to avenging his father's death.
Revenge is a funny thing. When a person is seeking vengeance for something history has a nasty habit of repeating itself, as demonstrated by the tragedy of Jinno. After nearly dying he was found by a group of monks called the "Empty Seven" Clan that rebuilt him using cybernetic parts and implants to he could live. Jinno took the name "Kuma", which means "bear" in Japanese, after the cybernetic mask he wears. That bear mask is a mirror image of a teddy bear that a young girl he knew from his childhood constantly carried that he believed died thanks to Afro's actions.
His heart burning for revenge against Afro and what he did, he agreed to stand watch outside of a mountaintop gate so he could one day challenge him when he arrived. When the day finally came, Jinno almost killed his old friend, but was instead cut in half at the waist and left to die. He would not be defeated that easily. He was again revived and repaired and rose to challenge Afro again. After a point Jinno had been repaired and augmented from various injuries so many times that he was far more machine than human. He had become mindless, an empty vessel that's only use was killing. He had let his hatred consume him until he had lost his last shreds of humanity. In order to reach his goal he stopped being
him.
Jinno's story is a sad one, a life destroyed by another's quest for vengeance that would spawn a similar hatred and malice in another as a result. His story is an object lesson in the vicious cycle of revenge. One person's actions to punish an enemy will inevitably cause another to hunt them in turn. It's a self-perpetuating cycle of death and self-destruction in which there is no escape.