William is evidently still in love with Yumi in Evolution. In X.A.N.A. 2.0, he is seen to be slightly flirtatious towards her by complementing her hair and attempting to deliver her love poetry in Mutiny. It is also revealed that she is the reason why he decided to become an agent. It has been suggested that they might be dating because they are both agents of AXE but this has not been confirmed. Here's how one fan site describes their relationship: "Yumi is a Japanese woman who lives in England. She works for AXE as an agent. William is an American man who lives in England. He works for AXE as an agent too. They like each other but don't say anything about it because they think it's not right." So there you have it, guys! This is what we know so far about Yumi and William's relationship in Avengers: Age of Ultron.