Mary (メアリ, Meari) is one of the three main characters in .hack//Quantum.
- Her appearance is nearly an exact duplicate of BlackRose's outfit. The main difference from the original is her long ponytail hair and a rose accessory worn on her left side of her head. Sakuya refers to it as a "BlackRose" type in a flashback
- The limits of Mary's seemingly boundless kindness are often tested by the impulsive Sakuya and cold Tobias. Once again she is forced to clean up the mess.
- Etou Eri (江藤衿, Eri Etou) is a female high school student living in Aomori Prefecture. She was invited to The World by her childhood friend Asumi. She has a caring and sincere personality.
Eri, Asumi, and Iori have apparently been playing The World together for a very long time, and appear to be medium-level players, at least high enough to fend off The One Sin with one hit. Skilled in combat, Eri is very quick thinking despite initially assuming the game to be for weirdoes, and even in earlier levels, she was shown to be a skilled player, memorizing enemy weaknesses and strategizing to make up for Asumi's clumsy blunders. Her devotion to helping Asumi eventually leads to her being infected after being PK'ed, and her body is trapped in the game, as some sort of Vagrant AI in the service of Hermit. This prompts both Iori and Asumi to rescue her. Then later free from her coma.
- In the first episode, particularly in the scene where Shamrock scolded her guild members about the bounty, upon closer inspection to the screen Mary's character name is listed as メアリ・リード (Mary Reed/Read) but it was not mentioned nor put in the credits.