Onyx is a silent assassin known to have crossed paths with Batman. She is a master swordsman. Some time later, she was recruited to the League of Shadows by Talia al Ghul (DCUAOM). She became a loyal second-in-command to The Heretic. After Batwoman and Batman broke up an interrogation of Chuckie Sol, a Made Man of Black Mask, Heretic and Onyx engaged them in combat in a warehouse. At Heretic's command, Onyx threw three knives into Batman while he was distracted with saving Batwoman. Heretic set off some explosives and Batman went missing. Over two weeks later, Onyx took part in the raid of Wayne Tech. Heretic and Onyx battled Batman (Dick Grayson) during the showdown. Back at the Sisters of Perpetual Grace convent, Mad Hatter was not making fast enough progress with brainwashing Bruce Wayne(Batman) (DCUAOM). Talia drew Onyx's sword on Hatter and implored him to dig deep past his trauma. Heretic disobeyed Talia's direct order to not capture Robin and brought him to the convent to steal his memories. Talia found out and became irate, slapped Heretic and went into a tirade.
Onyx was about to draw her sword but Heretic gestured her to stand down. To her dismay, Talia killed Heretic then ordered her to dispose of the body. Batman and Batwoman followed a tracker concealed on Robin's suit to the convent. After the front doors were breached by Batwing, Onyx attacked Batwoman, who took the fight to the bell tower. Onyx got her in a choke hold, but Batwoman flipped her over the edge as the tower and most of the compound collapsed as a result of Killer Moth and Firefly's pursuit of Batwing. She survived certain death and laid low for a week. After her plan to take over world leaders, corporate executives and military officials at the World Tech Summit failed and Batman broke through his programming, Talia made a retreat. Onyx was waiting in the transport, came up behind her and exacted her revenge. Batman, Robin, Nightwing, Batwoman, and Batwing watched as the transport crashed into the waters just outside Gotham.