Lithium

"'IF PEOPLE KNEW WHEN THEY WERE GOING TO DIE, I THINK THEY PROBABLY WOULDN'T LIVE AT ALL.' -Death, from Reaper Man by Terry Pratchett"

Lithium is one of the four Sysadmins, and is the ruler of what is referred to as the Underworld, or the Land of the Dead. She first appeared in a crisis involving a myth claiming he could destroy the Multiverse, but this was averted by Lithium and fellow Sysadmin Max. However, shortly afterwards Lithium was seriously injured by the Harbringer, who decided to cripple her after injuring Lithium in the past and causing her to have a weakened respiratory system, requiring the usage of a Black Iron Commando or an oxygen mask to breathe.

While the Black Iron Commando has since been destroyed when she was crippled, Lithium still retains the usage of an oxygen mask while not using an avatar to interact with the Multiverse. She currently spends most of her time with her fellow Sysadmins.