Eiri's possessive. Hiro knows that. That's why Hiro likes what he can get.
Eiri was possessive; everyone knew that, Hiro more than most. But he couldn't help it, and it's not like Shuichi discouraged him anyway. After all, what was a little groping between friends?
Hiro couldn't help but be attracted to Shuichi. He was, after all, his best friend since forever, and it wasn't easy trying to keep it hidden from someone as tactile as the pink-haired singer.
That was probably why Shu knew from the start.
He didn't have a chance; he knew that. He accepted it and found someone who could make him feel as wonderful as Shuichi could. Ayaka was beautiful and kind, and he could honestly say he was falling in love with her...but it didn't stop him from thinking about Shuichi - and how could he? He saw the little bastard every day, and getting a "HIIIROO!!" and a glomp was far too tempting.
But Eiri was possessive.
Hiro adored concerts. Performing live on stage for screaming fans that all loved him and loved what he did for them.
And he got to grope Shuichi.
Somehow, he couldn't manage to feel guilty. It was so wonderful: the thrill of the crowd; the adrenaline; the music! And Shu. Always Shu.
Shu dancing around onstage in the most ridiculously skimpy (sexy) outfits known to man. Shu wiggling and sliding his hand over his body in a one-boy show. And Shu dancing with him; taking the moves Nittle Grasper's Tohma and Ryuchi had shocked the world with and making them almost orgasmic. Shu's hands running over his stomach; Shu's cute little ass sliding against the front of his pants; Shu's mouth on his ear, hand in his hair, fingers unbuttoning his shirt.
And K even encouraged reciprocation. It was wonderful.
And it was nearly as wonderful when Shuichi next came to work; late as usual and positively covered in hickeys. Even though it reminded him how devoted Shuichi was to Eiri, it also let his imagination run wild on just how that mark on the back of his neck got there, and just why Shu was limping when he thought no one was around. It was delightful. To put it simply, it was Shuichi. That was all there was to it, really.
Hiro never did anything outside of concerts and daily glompings though; he knew what not to do with things that belonged to Eiri Yuki, and he actually respected that Eiri hadn't forbidden Shu to do anything with him onstage, though that was probably because he knew just how much Shuichi loved him, and how much he loved his career.
It kept Shu happy too - as long as Eiri ravaged him after a concert, he knew that Eiri had been watching, no matter what he said to deny it. Of course, this had the side benefit that the steamier Shuichi made it, the better the lay would be.
Hiro really couldn't argue with that kind of logic. In fact, he loved it.