With a great effort of will, you tear your gaze away from the creature's burning eyes and try to push the rising surge of fear back far enough so that you can not only act, but act rationally. And in this situation, with your magic the next best thing to useless, an unknown being of darkness bearing down on you - armed with both a fear-inspiring gaze and an alarming ability to absorb ki - and your most experienced and currently combat-capable ally telling you to run for it, there is only one rational course of action.
Maintaining your grasp on Altria's hand, you turn and run for your life, using both your ki and the fear that you could not completely suppress to lend extra speed to your retreat.
"Altria!" you shout. "Call Ambrose!"
"What do you think I'm doing?!" the British girl snaps back at you. You glance sideways, and sure enough, she's switched out her knife for her cellphone, which is already open and dialling. After a brief delay, Altria starts shouting into the phone. "Ambrose! Emergency! Find me right now!" She stops for a moment. "I do not care where you are! I need help! No, it does not matter that she has an identical twin sister!"
"Less talking, more running!" Lu-sensei barks at you both as he catches up with you.
"Aaaahhhh!" Briar continues to wail.
Cordelia... says nothing.
"Yes, that was Alexander's teacher!" Altria says. "Yes, he is running! You- Ambrose!" She stares at the phone in her hand for a moment, then snaps it shut, growling. "I cannot believe that man sometimes!"
"Is he coming or not?" you demand, ignoring the turns to continue running for the atrium. Quite aside from the speed and distance you'd lose taking one of the corners, the thing pursuing you is a creature of shadow; you can't help but feel that a huge room full of sunlight is the best possible defense you could hope to have against it.
"He is - and I quote, 'to see the boy's teacher running around like a headless chicken.'"
"Never mind that now," Lu-sensei says. "Run faster!"
You look back, and see that the shadow-man is pursuing you, its long, swift strides allowing it to keep pace, if not precisely catch up to you. Alarmed, you heed your teacher's command and channel more ki to your legs and core, further enhancing your speed. Altria keeps pace, although you dimly sense that her reserves are once again sinking towards depletion.