Yami no Matsuei, Tsuzuki/Touda, eternal commitment
Shinigami don't live forever, but he has to try. There are so many people depending on him, loving him, that he just has to. It took a long time for him to realize it. It took Hisoka and Touda to hammer the point home.
What would happen to his shiki without him? How would his friends in the Ministry carry on smiling?
No, he has to stick around, to take care of those most precious to him. If he died, what would happen to Touda? Would they send him back to prison to rot for another eternity? Or would they kill him the way Suzaku keeps threatening? Would Touda do anything to defend himself?
There's too many questions and not enough answers. Any of the others might be alright, depending on each other in their time of mourning. Touda wouldn't. He'd be alone again.
So Tsuzuki had to live. He'd been selfish, taking Touda from the darkness and claiming the shiki as his own. Fighting to keep what he'd found. He'd been selfish to depend on Touda's presence and quiet, calm love.
The steady, thrumming beat of his heart at night, the callused caress of his large hands are imprinted in Tsuzuki's mind. The pleased little hitch in Touda's breath as he's filled, silken muscles clamping tight around Tsuzuki's length, hips grinding down to take as much as he can.
He was selfish, but taking on the heart of another was a life long commitment. So he had to live, for as long as possible.