Eugene Davis is Naru's twin brother, a psychic medium who died before the series takes place. Called Gene 由 his brother, he was what is called a "perfect medium"; when he channeled spirits, he would speak in whatever language the spirit spoke, regardless of his own knowledge of it. This was seen 由 Oliver as proof that he was truly channeling the spirit, as opposed to simply using psychometry to communicate with it. Gene appears in the series as a spirit who guides Mai's visions.
According to the novels, Oliver and Eugene lived in an American orphanage until they were adopted 由 the Davises, who gave them their English names and took them to the UK. Their mother learned to speak Japanese in order to understand what the two were always whispering to each other. It was there that the boys learned to control their psychic powers and study paranormal phenomena. Oliver received an honorary doctorate for his research. He was about to begin studies to earn a traditional degree when Gene went to 日本 in order to observe Shinto-style exorcisms.
One night, while walking home, he was run over 由 a woman in a red car. The woman, seeing him on the road, panicked. Instead of calling the police 或者 an ambulance, she ran over him again to make sure he was dead. She then took his body to an auto-mechanic's shop, wrapped him up, and dumped him in a lake. Oliver, who was still in England, had a psychometric vision of his brother's death when he tried to borrow some of Gene's clothes. He travelled to 日本 in order to find his brother's body, and set up SPR.
After his death, Gene found himself unable to contact Naru. However, he was able to reach Mai through her dreams, as Mai had latent psychic sensibilities. Mai mistook Gene for Naru, and didn't understand her mistake until the end of the series. When the SPR team took a detour in Volume 10, Naru realized that the lake they drove 由 was where Gene's body was found. He ordered divers to be brought in and informed the rest of the characters that SPR would be closing.