"Settle down class" Came an eerie, impressively low voice that carried through the entire room without any real sense of where it had originated from. Suddenly, behind the podium a silhouette began to float up, eventually revealing a long-faced (literally), man with grey-blue, transparent skin and a less than satisfied frown. As he became tangible again he pulled papers from under the podium and pounded them on the surface before him to straighten them out. After a long moment to take him in, it became apparent who he was: Wraith. Wraith was one of the heroes created through the newly attempted heroic recovery program. This was a system that rather than imprison villains who escape again and again they conduct an intense background check to see what made the person go into the world of the villain, in Wraith's case: a destructive home environment. From there they offer to help them in return for the villain turning into a hero. Wraith was the staple of this, becoming their mascot of sorts. After only a month of therapy was he changed and willing to give up many of his terrible habits.
"Alright class, settle down" He growled almost intimidatingly. He stared them down angrily before stepping through the podium. If it was no already apparent, his ability was to turn him, and a spare few other items intangible, though in doing so he puts a strain on his mind and is unable to interact with his environment. Placing the papers on the first student's desk before them all was a paper blank save for one question: 'what is a hero?'. Straightening his grey suit and pants, similar to what the students wore he slowly cranked out a smile that looked almost painful. 
"I'm your teacher, my hero name is Wraith but please, call me Mister Walker. Now then, We'll go down the line and say our names, our quirks and a little something about ourselves, how does that sound?" He spoke, and despite his appearance and how low his voice was, it was smooth and calming like a father consoling its child. It had a pinch of sorrow in it as if he felt that he was doing wrong to these students, but perhaps that was yet to come. Regardless it was covered by his stoic lack of any other emotion. 
"I'll go first for you all. My name is Xavier Walker, my quirk is called ghost as it allows me to move through things and I enjoy cooking, now then, who is willing to go next"