Fate/Zero 2nd Season

Synopsis

After leaving the island, Kiritsugu began living with Natalia, who trained him to become a mercenary like her and travel around the world as a hired gun. Due to his unique magic, Natalia removes several of Kiritsugu's ribs and uses them to create sixty-six magic bullets that have a devastating effect against magi. Natalia and Kiritsugu are assigned to kill Odd Dvorak, a Dead Apostle mage who controls bee familiars that turn their victims into Ghouls. While Natalia boards the plane that Dvorak is taking from Paris, Kiritsugu heads to his destination of New York to kill the mage's associate there. Both Natalia and Kiritsugu successfully eliminate their targets. However, Dvorak was concealing bees in his body which turn all the passengers and crew into ghouls. Natalia manages to get into the cockpit safely, but with the plane filled with ghouls, she asks Kiritsugu to do something for her. He surprises Natalia by saying he already has something planned. As her plane draws closer to New York, Natalia and Kiritsugu talk via radio, reminiscing about the time they spent together and the bond they shared. When her plane is in view, Kiritsugu does what he believes will save more people: to prevent a Ghoul infestation, he blows up the plane with a Stinger, killing all the Ghouls on board and Natalia along with them. Before he pulls the trigger, he tells her he was glad to have her as his mother. As the plane explodes, Natalia is seen smiling. Kiritsugu collapses in grief over losing another loved one.

(Source: Wikipedia)