Three years ago, Serizawa was troubled with about his psychic powers. One day, he was visited by the boss, Suzuki Toichiro. Serizawa ends up trusting him since he's the first person to understand what he's going through. But Mob then brings up the fact that Serizawa is being used and tells him, "I'll be your friend." Hearing Mob say that, Serizawa... 

Meanwhile, after defeating Sho, the boss starts gathering up the energy he was sharing with his followers and turns into an energy monster.
I guess I can see how you two
are master and student.
أظنّني أفهم كيف أصبحتما مُعلّماً وتلميذاً
Jetzt weiß ich, warum du dich
als sein Meister bezeichnest.
Je vois pourquoi tu es son maître.
Sì, ora è decisamente ovvio che siete maestro e allievo.
Eu acho que entendo como vocês 
são mestre e discípulo.
А ещё назвался
учителем этого сопляка.