Farfarello, whose real name is Jei, is a supporting character from the anime series Weiß Kreuz. He is approximately twenty years old and was born in Ireland. His name is derived from a demon in Dante's Inferno, a choice that reflects his nature and literary awareness. He is a member of Schwarz, a rival assassin team to the protagonists.

Farfarello is often described as demented due to his enthusiastic embrace of violence, which he inflicts on both others and himself. His most defining characteristic is an all-consuming, pathological hatred of God. This vendetta stems from a traumatic childhood revelation: he discovered that Sister Ruth, the nun who was his teacher and a figure he admired, was in fact his biological mother. The psychological shock of this betrayal, combined with learning that his adoptive parents were not his real family, caused him to murder his adoptive parents and sister. He blocked out the memory of committing the act, instead believing that God had taken his family from him. This event shattered his faith and twisted into a mission to kill the Christian God, a goal he pursues by torturing believers and desecrating religious symbols and places. He sees himself as a victim of divine cruelty, and this perceived victimhood justifies his own brutal actions as acts of revenge.

In combat, Farfarello is a formidable and unpredictable fighter. His most notable ability is a complete inability to feel physical pain. While he can still perceive tactile sensations such as temperature and texture, the signals that would normally register as painful do not bother him. This allows him to push his body far beyond normal limits, continuing to fight and use his muscles even after sustaining severe injuries that would incapacitate anyone else. He is strong, agile, and highly skilled with sharp weapons, favoring a dagger-like pick that can extend, along with various blades. He has even demonstrated the ability to hide needles within his mouth to use as concealed weapons. His fighting style is relentless and berserker-like, showing no regard for his own safety. He is covered in numerous scars from his many battles and self-inflicted wounds, and he wears an eyepatch over a left eye that he removed himself.

Farfarello's personality is characterized by his isolation and instability. He holds no genuine affection for others and finds concepts like friendship to be laughable. His teammates in Schwarz, including the clairvoyant leader Crawford, the telepath Schuldig, and the young psychic Nagi, are individuals he merely tolerates because their violent goals align with his own. He is often kept restrained by his team when not on a mission. Despite his insanity, he is intellectually bright, speaking multiple languages and possessing an encyclopedic, if biased, knowledge of Christianity and Catholicism. His mind, however, is severely damaged due to extensive torture and experimentation by the Rosenkreuz organization, which sought to weaponize his pain insensitivity and psychotic tendencies. This has left him prone to auditory and visual hallucinations.

There is a notable romantic development for Farfarello in the Dramatic Image albums, a series of audio dramas. In this storyline, Schwarz encounters a young witch named Sally Schumars who is fleeing the same Rosenkreuz organization. Farfarello and Sally fall in love, as she is able to make him feel emotions once again. At the conclusion of this arc, he parts ways with Schwarz, leaving with Sally with the team's blessing.

Within the main anime storyline, a pivotal confrontation occurs with Ken Hidaka, one of the members of the rival Weiß team. During their final battle, Farfarello is stabbed in the head by Ken's clawed weapon and subsequently drowns. His legacy within the narrative is that of a tragic figure whose humanity was destroyed by manipulation and trauma, leaving behind a being of pure, painless, and intelligent rage.