KirIri

Kiritsugu x Iri is the Het ship between Kiritsugu Emiya and Irisviel von Einzbern from the Fate fandom.

Canon
Kiritsugu Emiya met Irisviel when she was created inside a tube. Through their initial interactions, he discovered that she was useless and Kiritsugu expressed his frustration to Jubstacheit von Einzbern (the creator of Irisviel) regarding Irisviel's lack of understanding to protect himself and interact in society. So Jubstacheit decided to prove Irisviel's durability by casting her into the deserts of the Einzbern forests. Disgusted by Jubstacheit's actions, Kiritsugu rescued her and personally began educating Irisviel about current society and the modern world so that she could develop a sense of identity. Her rapid development and unexpected insights into humanity surprised Kiritsugu and they fell in love with each other. However, Kiritsugu knew that their love would end up in tragedy, as he would have to sacrifice her for his ideals.

Fanon
On AO3, Kiritsugu Emiya x Irisviel von Einzbern is the second most written ship for Kiritsugu and the second most written for Irisviel as well. It is the seventh most written ship within the ship in the Fate/Zero tag.