Caynz

Caynz (カインズ) is one of the 10,000 players trapped in the online game Sword Art Online. He's a former member of the guild Golden Apple and teamed up with Yolko to find out who killed Griselda.

Before A Murder Case in the Area
He was part of a small guild called Golden Apple, which only had eight members. One day they found a rare-drop item and they voted to decide what to do with it, Caynz was in favor of keeping the item, but loosing in the voting three to five, they decided to sell the ring, but when the leader of the guild depparted, she never came back, and they found out that she was dead.

A Murder Case in the Area.
When Kirito and Asuna were going to have dinner, Yolko screamed and Caynz was found hanging outside the church with a weapon piercing through him. Kirito and Asuna try to save him, but he dies before they reach him.

The next day it was revealed that he wasn't dead that, along with Yolko, they faked their deaths to trick Schmitt and found who killed their former leader Griselda. After they record Schmitt's confession of being an acomplice they're surrounded by the top three of the Laughing Coffin guild, but are saved by Kirito, it's later revealed that Grimlock was who planned Griselda's death and wanted to kill them to finally cover the incident.

Trivia

 * In the light novels, when Yolko was asked how to spell Caynz's name, she spelled it as "Kains". Kirito and Asuna then went to the Monument of Life to confirm his death and saw that "Kains" did die by piercing DOT and also at the same time as when they saw Caynz's "death."  This was to mislead Kirito and Asuna into thinking that he actually died and to make the rumors of player kill in safe areas possible.