A low ranking member of the Mafia working under Rod Ross, Neylon was involved in drug trafficking and illegal weapons sales. Despite four separate arrests, he was cleared every time due to lack of evidence.
When the Mafia, led by Ross and Mello, manages to extract the Death Note from the Japanese police, it ends up in the hands of Neylon who becomes the new owner, even though Mello handles it several times while examining it for clues that could lead to Kira.
After Sidoh tracks down his Death Note at the Mafia's hideout, he gets Neylon to see him and persuade the others present to touch the Death Note and also see him. From Sidoh, they learn about the Shinigami Eyes trade which enables a human to see the names of others in exchange for half his life expectancy. Mello tells Neylon to do the trade. He initially refuses but Ross then threatens to shoot him dead on the spot if he doesn't — Ross even further tempts Neylon by telling him that doing so would make him his right-hand man.
Using her own Shinigami Eyes, Misa Amane eventually identifies Neylon as another Death Note owner since, while going though FBI files of known Mafia men, she can see his name but not his life expectancy. She passes this on to Light Yagami who uses the Death Note to have Neylon mail him the address of Mello's hideout.
Light then sends a US Army Special Forces team to raid the hide-out but their face-covering helmets are removed by the invisible Sidoh. Their faces are picked up by security cameras and relayed to TV monitors: Neylon can now see their names and passes them on to Ross who writes them down in the Death Note, killing the soldiers. The Mafia then evacuates to another base.
(In the scene where he reads out the names and when he and the others are escaping in cars, Neylon has his hands behind his back and is wearing handcuffs. Although it is not specified why this is the case, it could be that Mello and Ross consider him and the Eyes as too valuable to let him wander off. He may have been caught after posting the letter to Light.)
Light has already set Neylon to die at 23:59 on November 10 2009. Following the failure of the initial raid, he organizes a new one with the Kira Investigation Team which is carried out at midnight on November 11 after Neylon and most of the other Mafiosi have been killed by Misa's Death Note.
- In the anime, Neylon's Eye trade and the first attempt to retrieve the Death Note were not included.
- In the anime, Neylon didn't kill the Army because that part were not included
- “B-Boss… is this ugly-looking guy in the costume a new recruit or something?”