After getting saber to drink from the holy Gail Kiritsugu and saber worked together and defended Gilgamesh and then saber destroyed the Gail. After all the carnage was over Kiritsugu wanted saber to watch illya for a while a bit but Irisviel wanted to travel the world and she wanted (forced) saber to go with her. Years later the two returned to speak with Kiritsugu about her new assignment. She was to watch they're new adopted son Shirou and prepare find for the next grail war(while Irisviel and Kiritsugu did some more traveling) it didn't take long for Shirou to get his command seal or for the two of them to fall in love