WataHima is the name given to the romantic pairing between Watanuki and Himawari.
Since the beginning of the series, Watanuki has always had a crush on her and Himawari have some feelings for him as well and consider him a very special friend. They have been friends since they met, both are in the same class and have lunch together so it can be say that they spend the most of their time on school together. Before meeting Doumeki, Himawari wasn't afraid of hurting Watanuki with her bad luck. They used to stick together in the school often sharing their lunches, she also touched him many times and even asked him to go along with her to a cafe grabbing his arm and practically forcing him to go out with her.Despite he is very obvious about his crush on her, Himawari doesn't point it out though she would easily realize it. Whenever Watanuki is asked why he likes Himawari, he answers that it is because she is kind and cute and even though these are good traits in a person, it is not enough reason to be in love with someone and so all of his friends know that this is not real love but just a crush. When Watanuki first told Yuko about Himawari, Yuko told him that Himawari might not be his "lady luck/ lucky lady." However, Watanuki does not give any importance to what others say and keeps on trying to impress Himawari with smarts or courage. They sometimes shared conversations about supernaturals things that Watanuki lived everyday. While being a bad experience for him, Himawari's love for the supernatural makes her enjoy her time with Watanuki. She also cares for him a lot, some of Yuko's works and commisions force Watanuki to risk his own life making Himawari even more worry for his sake. Sometimes, Himawari tries to help Watanuki with his tasks but he always refuse so she makes a pinky promise with him and asks him to never force himself too hard.
Himawari shows some interest on him but nothing that says that she is in love with him until the Vol. 10 when Watanuki falls out of the second story window of the school and nearly dies until Doumeki brings him to Yuko's shop where she heals him. Himawari confess to Watanuki the truth about her bad luck and many of the bad things that happen to him are because of her. Himawari had been born with a bad luck curse at birth which meant that she brought bad luck to those whom she mets, talks to, or touches with the exception of her parents. She also says that she has been waiting the whole time when he was going to find out and talk to her about it. Himawari then thanks him for all the lunches he prepared for her and tries to say goodbye for the last time but then Watanuki stops her, ignoring all the things she said and tell her that he'll make it up to her with his cooking. She asks him if he really listen what she just say and then he answer her that even though she is bad luck, he feels very happy when she is around like if he was in heaven and he'll always felt lucky to have met her. Himawari tries to warn him that he may died the next time but then Watanuki said: "Because I love you Himawari-chan, I'll never do anything to hurt you or to make you cry". Himawari does not answer to his feelings calling him an idiot but then she asks him to cook a cake as a compensation and eat it alone with her.
Later outside the shop, Himawari leaves crying of hapiness because Watanuki survive and despite everything that happen, he doesn't hate her and even has feelings for her. She said it was the first time that someone said "I'm very happy to meet you." and then reveals to the public that her payment to save Watanuki's life was to take his scars that will remain after the wounds are heal. In this scene, the public can see that Himawari's feelings for Watanuki are beyond friendship because in japanese culture, the women who have scars can't be consider beautiful and affects their chance to marry giving her a heavy weight she must carry for her entire life. Watanuki asks Yuko if there is a way to remove Himawari's curse and Yuko says that she can but the price it will be all her happiness. She asks him if he is going to pay the price but he says that if he hurt himself for Himawari's sake then she won't be happy at all and it will be more painful for her than himself. Watanuki decides that the only thing he will do for Himawari is to continue being her best friend and making her truly smile everytime. This proves that his feelings for Himawari are not just a crush for making the choice to keep loving her from the distance as a friend. Yuko does agree to help Watanuki with his relationship with Himawari by giving him an egg and telling him to sleep with the egg beside him and whatever he wants to emerge out of the egg, it will appear. In dreams, Watanuki wishes strongly for Himawari's happiness and so Tanpopo is born, a bird that is immune to Himawari's bad luck. Then, Watanuki gives the little bird to Himawari and they go back to being good friends.
They spend more time together since Watanuki is being carefully after being with her and becomes smart enough to realize when Himawari is trying to avoid him and he doesn´t give her the chance to run away from him. Now that she doesn´t have the chance to escape from her friends, she decide to accept his invitations to spend more time together, including Doumeki. In her last physical appearance in the manga, she cook again after many years for Watanuki and asks Doumeki to eat her cooking along with him in order to protect him from her bad luck. Himawari's seems to be trying to become more close to Watanuki since she have finally developed feelings of love for him. Since she couldn't see Watanuki anymore after he decide to become the master of the shop, she would have felt in love with him before.
In xxxHolic Rou, Himawari and Watanuki grow apart because Himawari misfortune is bad for the shop and for her own sake so she promises that she will only visit the shop on his birthday. Despite being separate, Himawari shows to be deeply in love with Watanuki and so he has developed true feelings for her as well. They start a long-distance relationship and talk via telephone. 10 years later, Himawari gets marry with somebody else who knows about Watanuki and accept their relationship but they are not able to meet each other because her husband can´t enter to the shop and Watanuki can´t leave.
With Himawari's marriage, this pairing finally comes to an end where the two characters ends in a "more than friends, but less than lovers" relationship. Since xxxHolic is still "on going" it is possible that Himawari makes an appearance again in a continuation of xxxHolic series and so continue the pairing.