Ozen the Immovable is an elite White Whistle who lives at the Observation Base on the second level of the Abyss where she commands a small team of cave raiders known as "The Layabouts." Ozen was a mentor and a close friend of Riko's mother Lyza.
Ozen is a peerless fighter—her unique relic "Thousand Pins" grants her superhuman strength, speed and longevity (even though Ozen appears to be young, she's attained the rank of a white whistle more than 50 years back). She's over 2 meters tall and has a peculiar hairstyle which conceals the scalp deformations caused by the extended exposure to the Curse of the Abyss.
Ozen has absolute control over her facial expressions and her actual feelings (or lack thereof) cannot be guessed with any certainty. The reasons behind her actions are unknowable as well—Ozen rarely bothers to explain herself and even when she does it's impossible to know whether she's telling the truth or just toying with the audience.