This is simple and short…
Shura is apparently an old student of Fr. Fujimoto and she was asked by him to train Rin. However, she has orders from the Vatican to investigate what Fujimoto and Mephisto were doing. And her findings revealed that they’re hiding Rin, known as Satan’s son and were training him as a weapon against Satan.
Oh man! I’m losing my Gendou glasses!
Like Rin, Shura has some problems with Fujimoto and it seems she looks him up as a father figure. But when she found out that Fujimoto is hiding something from her, she’s clearly pissed at him. And now, she’s in charge of training his adoptive son who is Satan’s son and also kill him since he’s a threat.
Now, I’m your Defense Against the Dark Arts teacher
But Rin vows to her that he will prove to everyone that he will kick Satan’s ass and be the most powerful exorcist. Oh and also to prove that his dad did the right thing to protect him. This is when Shura realizes that Fujimoto treats Rin as his own son. So, now Shura decided to train Rin and not to report this to the Vatican. But she doubts Mephisto’s motives which is bringing peace between the humans and demons. He’s still a mystery.
So, you’re still not angry for wreaking your statue?
BTW, here comes the new OP and it’s slightly spoiler-ish. Like that guy in white. You’ll know who he is later on. But the song really kicks ass. And the ED is plain but I like how they use the transition. But the song is catchy.