Lyza the Annihilator
Lyza's one of the most celebrated white whistle divers ever, known for pushing deeper into the Abyss than almost anyone and uncovering major secrets about how the place actually works. She trained Ouzen, who'd go on to become a powerhouse herself, and she's also Riko's mother—a detail that becomes pretty important to the story since Riko ends up following in her footsteps.
Beyond her famous apprentice, Lyza also took on a student named Jiruo at some point during her diving career.
The thing is, about ten years before the events of the main story, Lyza descended into the Abyss and never came back. That absence haunts a lot of what happens later.
Content compiled by AnimeList.moe from publicly available sources.
