Moral Event Horizon: Tadaomi killing Shou/Rei's father is only one of these. Actually, he pulled something even worse earlier: he is the one who killed the Mizumori parents (his own aunt and uncle, who by all accounts were really sweet people), in hopes to both awaken Mio's powers and have her forced to live with him.
And how he destroys a plane with his powers solely to murder Shou. Killing everyone but him instead.. which includes the recently broken Miyabi.
Nightmare Fuel: How Tadaomi murders the Narumiya patriarch. Via setting him on fire. On page.