xxxHolic, Watanuki/Haruka (and Watanuki/Doumeki), the best part is how he's nothing like Doumeki
The differences between the two weren't that monumental. In fact, if a random stranger were to walk by, they would see no difference. Only someone who knew them well could tell them apart. And, while most people would marvel at how alike they were, Watanuki spent his days counting the differences.
It never looked right when Doumeki smiled. There was just something about that boy that made smiles seem foreign and forced. The most he could manage was a slight smirk, and even that made Watanuki wonder if something else was up (even though it was usually nothing more than Watanuki's imagination). Haruka, however, smiled all the time, and Watanuki never questioned it. Haruka's smiles never had that weird feeling that Douemki's did. And, even though Haruka usually had something more hidden behind those smiles, Watanuki never suspected a thing.
Doumeki was a protector. Even though Watanuki often yelled at the boy, he also knew that he would always be safe around him. Doumeki would gladly use his body to shield Watanuki from danger. In fact, he had already done so. No matter what danger was thrown at him, Watanuki was sure that Doumeki would be there to get him out of trouble. Haruka, on the other hand, was a nurturer. He was the one Watanuki went to when he needed advice, or if he just wanted someone to be there.
When it came to words, Doumeki always knew just what to say to piss Watanuki off. Often all it took was as few as three words at just the right time to send Watanuki off on a tirade. And then Doumeki had the gall to plug his ears to shut out the noise of Watanuki's ranting. But with Haruka, Watanuki never found himself getting angry. Haruka spoke the truth, but it was never upsetting. In fact, it was usually the opposite: Watanuki usually felt better after talking to Haruka.
The biggest difference, though, was in how they loved him.
With Doumeki it always started out with a fight. Either Watanuki was already angry, or Doumeki said something to make him angry. And then, in the middle of his ranting, Watanuki would find himself quickly interrupted by a kiss from Doumeki. That one kiss would quickly grow to many short but forceful kisses as they fumbled around with their clothes. Then Doumeki would taunt Watanuki, giving him gentle touches that just made him want the other boy even more. It was never enough, and Watanuki would be practically begging for it before Doumeki gave him anything. From there it was quick, rough, and mind-blowing: once Doumeki got going, he didn't stop for anything. These nighttime activities would often leave Watanuki sore for a day or two afterwards, and he would have to wear high-collar shirts to cover the marks on his neck. Loving Doumeki was very quick and rough, but it was passionate.
With Haruka, though, it was the exact opposite. There was no yelling or flailing: instead it would start with kind words. Haruka would say something that surprised Watanuki, or even something that made the much younger boy blush. Then, with that smile playing at his lips, Haruka would lean in and give Watanuki a soft kiss. This one kiss would continue for some time, and they would part only to take a breath. There was no struggle to get naked as quick as possible, either. Haruka would slowly and carefully undress Watanuki before gently guiding him to lay down. Haruka would run his hands over Watanuki's body, eliciting all sorts of shivers and lovely sounds from the boy, but he never drew it out to the point where Watanuki was so needy that he had to beg. Haruka was very responsive, and he took care of every little thing Watanuki needed. And when they finally reached the end, Haruka always held off and let Watanuki release first; seeing the younger boy arch up off the bed slightly in pure ecstasy was intoxicating to the older man. Loving Haruka was slow and sensual, but it was mind-blowing.
Some people said they wanted to be with twins because being with two people who were exactly alike was exciting. Watanuki never understood that. Doumeki was nothing like Haruka, and Haruka was nothing like Doumeki. They looked identical, but their personalities couldn't be any different. And that, Watanuki decided, was the best part of it all.