Aozaki Aoko

One of the five existing Magicians. It seems she hates the alliteration in her full name, and gets mad when people call her by it.
Though she is relatively affable in Tsukihime, she is actually a merciless person.
As for why she's a Magician, it's because she arrived there at the end of a long and arduous road. If that's not a clear answer for you, please refer to Kara no Kyoukai. Well, it might still be unclear even if you do that, though…
She had such a large influence on the young Shiki that to this day she is the only person he calls “Sensei.”
Though her appearance seems to be the spitting image of the inverted Akiha, the truth is she actually has black hair.
…Wait, wouldn't that make her even more like Akiha!?
Within the Association, she is known as the Magic Gunner, Miss Blue. Her abilities as a magus are below average, but there are none more talented when it comes to destruction.

Tsukihime Data Collection: Tsukihime Dictionary
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One of the five existing Magicians. It seems she hates the alliteration in her full name, and gets mad when people call her by it.
As for why she's a Magician, it's because she arrived there at the end of a long and arduous road. If that's not a clear answer for you, please refer to Kara no Kyoukai. Well, it might still be unclear even if you do that, though…
She had such a large influence on the young Shiki that to this day she is the only person he calls “Sensei.”
The story of Tsukihime begins with Aoko and Shiki's first meeting. At that time, she seemed to be an amiable older-sister type, but generally her stance is to avoid getting too involved with other people.
Ever since becoming the Aozaki heir, she has lived the life of a rootless wanderer, roaming the world with a single trunk in hand. Her meeting with Shiki was merely a coincidence, akin to making friends with a local child in the midst of a long journey.
Within the Association, she is known as the Magic Gunner, Miss Blue. Her abilities as a magus are below average, but there are none more talented when it comes to destruction.
Though she is an important person to Tohno Shiki, she only has a minor role in the story of Tsukihime. The incident where she takes the leading role is a story for another time.
In Melty Blood Re-ACT, she appears as a hidden boss. As expected of someone with the nickname Magic Gunner, it's like fighting a living artillery battery. Also, maybe it's because she's not really taking it seriously, but her apathetic voice is pretty great. At first the production staff was a bit doubtful about the performance, particularly her monotonous “Oh, I guess I lost,” but eventually it grew on them. A lot.

Tsukihime Dokuhon Plus Period: Tsukihime Dictionary Revised
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One of the five existing magicians.
Though she is the legitimate heir of the “distinguished” Aozaki household, she's currently wandering around the world with a single trunk in hand. Her magecraft attribute is one specialized for breaking things, so she's not very good at healing, construction, and restoration sorceries. Known as the “Witch of Destruction,” she's not particularly versatile, but is second to none when it comes to busting out of hopeless situations.
It was due to her influence that the young Tohno Shiki was able to grow up normally despite being burdened with abnormal eyes. Therefore to him, she is an existence akin to a respected former teacher.

MB Act Cadenza PS2 Manual: Tsukihime Dictionary