Touko Aozaki [Person's name]
Aoko's older sister. She studied sorcery under her grandfather, but murdered him over the shock of having the Aozaki inheritance usurped by her younger sister and fled to the Association. Unlike Aoko, her abilities as a magus are top class. She has even received a sealing designation due to her status as the world's greatest puppet master.
She does not appear in Tsukihime. However, she is a key figure in Kara no Kyoukai, which intersects with Tsukihime. Tohno Shiki's mystic eye sealing glasses originally belonged to her.
In retaliation for having her prized mystic eye killers stolen from her, she's been making an effort to buy as much stuff as she can under Aoko's name. Then, even the Association has entered the era of e-commerce?
…Even though there's a high chance of her location leaking out if she keeps it up, it seems that revenge against Aoko even takes priority over her own self-preservation. Geez, Touko, you should try to be a little more mature.
By the way, her name shows up for just a second in Fate/stay night, too. Is she secretly trying to win the prize for perfect attendance?

Tsukihime Dokuhon PlusPeriod - TSUKIHIME Dictionary: Aozaki Touko [Person's name], p.175