She's part of the Black Cats of the Full Moon, a guild made up mostly of computer club members from the same high school—with Kirito as the exception. In the game, she fights with a two-handed spear, though her level lags noticeably behind her guildmates.
What's interesting about her is how she ended up leaving the Starting City almost by accident. She never actually planned to venture out, knowing full well she'd probably die since she's genuinely terrified of monsters. But she went anyway. Kirito's observed that the two of them share something: they're both socially awkward, they shut people out, yet they're equally afraid of being alone. It's that contradiction that defines her in a lot of ways.
Content compiled by AnimeList.moe from publicly available sources.
