Fate Zero S2 Ep 6: Terror in the Sky

Emiya had a surgical operation done by Natalia which enable him to cut mages' magic circuits with a special kind of bullet created from his ribs. He recalled that she took him in and train as a hired killer for both the church and Mages association.

During one of the mission, Emiya tried to save a father and his son but Natalia stopped him and got the father and son killed. Emiya thought that by killing his own father, he could prevent another tragedy from happening however Natalia suggested that unless he killed all the bad people in the world, it might work.

Emiya's smoking habit is influenced by Natalia

Later, Natalia received a new target-Odd Vorzak. A mage who used bee familiars to create zombies out of people. They spilt up to kill Vorzak and his allies. Natalia board the same plane with Vorzak while Emiya went to New York to assassinate his allies.

They both successfully killed their target and destroy the bees in Vorzak's suitcase. However Vorzak's dead body released a swarm of bee familiars which infected the people on the plane, turning them into zombies.

Natalia fought her way through the cockpit and secured the controls. However the plane will be landing in the airport in fifty minutes. Emiya drove a boat to where he could see the plane. Both of them reminiscing about how she trained him years ago. He fired a Stinger Missile at the plane killing Natalia and everyone on board.

Emiya began to cry as he has to kill another close kin in order to prevent the plane from landing and answered Shirley's question of what kind of person will he be when he grow up...

The second half of Emiya's past and we can see how bitter and grey he has become throughout the years. The zombies in the plane remind me of that bad horror movie-Dead Flight but surprisingly Natalia is capable of getting through the zombies and entered the cockpit. However both her and Emiya knew that if the plane landed, the zombies will escaped and killed more people which is why, he has to destroy the plane with Natalia on board.

I guess now Emiya is determined to kill every last mage to prevent another tragedy but I think he changed after meeting Iris which in the next episode, we are having another flashback but more of the rest of the characters before the Holy Grail War.