Genma knew exactly why he chewed on senbon. At first, it was because he couldn't find any toothpicks, and he had eaten a bit much popcorn, getting it caught between his teeth. Days afterwards, he'd become attached to chewing on the shinobi-issued needles. As things started to heat up between himself and a silver-haired ANBU captain, he found himself cutting his lips with the weapon.
Kakashi was never sure why the young man did what he did. He'd learned at a young age not to put weapons near his face; kunai practice at the academy had taught him that well, along with not putting an apple on his head. He cringed at the thought of the metal point of the senbon between his teeth.
However, he rarely minded when his lover would lick his lower lip to capture a stray droplet of blood. Especially when he would lean forward and kiss the wound better in front of his team. It was becoming quite a habit for Kakashi to kiss his injuries better, but he didn't mind. However, he told the other ANBU to watch how he held the needle between his teeth and that if he wanted kisses outside of the bedroom, all he had to do was lean forward and press a chaste kiss against his mask.
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Standard disclaimers apply.
Written for Rodick.