A/N: I never thought Yamamoto would start smoking, since he seems pretty concerned with being healthy. However, a lot of fanfictions and fanarts have TYL!Yamamoto smoking, so I got to wondering what might drive him to it. I came up with this. However, I still think that it would only be a temporary thing. He'd only smoke when he missed Gokudera.
This little bit would be after they broke up (before they got back together, of course).
Yamamoto listened to the sound of the wind whistling past the windows below him. He pulled the cigarettes out of his pocket and slid one of the shafts into his mouth, then got out his glinting metal lighter. The young swordsman covered the end of the cigarette with his left hand to shield it from the chilly night wind and lit it. Yamamoto drew a long breath through the cigarette, and started to cough. He would never get used to them, but...
He thought about the first time he had smoked. The box had been left on one of the chairs. Yamamoto knew perfectly well who they had belonged to. He had taken them on some mad impulse to have something more of Gokudera with him. The teenaged boy had had no intention to smoke them, but when he found himself unable to sleep with thoughts of the bomber riddling his mind, he had come up onto the roof and found them in his pocket. The young swordsman had taken one of the cigarettes from the boxes and gazed down at it. He wondered how Gokudera could do such a disgusting thing... it had always left a bitter taste in his mouth when they had kissed. When he'd tease Gokudera's lips apart and drive his tongue into the Storm Guardian's mouth as their bodies were laced around one another. He found himself lifting the stick to his lips, and searching his pockets for the lighter Gokudera had left in his house one day after school in what seemed like ages past. Yamamoto tried to light the cigarette, but found the wind put out the small flame on the lighter before he could reach the end of the shaft. He tried again, successfully. It smelled bad, but he placed one end to his mouth and took a breath. The smoke hit his mouth and lungs and he choked, and coughed. The feeling was horrible—as if his airways were shutting to not allow the smoke within. He tried again, with the same result, but eventually managed to take a full breath and let it out without gagging. And that was how it had started.
He was not addicted to the cigarettes themselves, but to the familiar acrid flavor it always left on his tongue. "Gokudera..." he whispered into the near-silent night, and took another drag from his cigarette, pretending for just a moment that the taste of ash in his mouth was from a cigarette held in a hand other than his own.