Summary: Tenzo tries to fade away. Gai refuses to let him. [Gai/Yamato, yamagai]
Square One
And even if Tenzo would care about his birthday, he still did not know when it actually was. After all people without names did not have birthdays either. He just had gotten assigned a birthday date on the day he had been rescued away from the lab, because that was the way things were supposed to work. No matter the danger, blood and tension involved, if Konoha had practice in anything then in applying the administrative processes needed to keeping the village functioning without disturbance. (The day he had been rescued was also the day his saviours had gotten fully aware of the way Tenzo could be useful to the village. He held no illusion on that part.)
If you wanted to live among other humans you needed at least a minimum amount of background information to do so. Coming out of the lab, Tenzo hadn't had any, hadn't even been able to answer the question if there ever had been anything, something that had gotten lost, or a blank space to begin with. Arriving in Konoha he had needed his minimum amount of background information. So he had gotten it. At least whoever had been in charge of assigning him new personal data had been sensible enough to pick another date than the one of the very day they had found him. At least like this Tenzo wasn't forced to remember the time at the lab and everything connected to it more often than necessary: Some things you'd just wanted to pretend to have forgotten, even when in reality the memory was sharp and clear. (Forgetting things was difficult the more you tried to make it happen.)
Either way, the result was the same: Tenzo had gotten a new date for his birthday, a birthday that wasn't his. Had to keep the date in mind anyway because sometimes you were given no choice but had to tell people an answer when they asked you about your date of birth. (If anything Tenzo felt more constructed than born but he was cautious enough to keep these kind of thoughts strictly to himself.)
He even went so far as to avoid telling this random date to the people he worked with closely through danger, blood and tension. So, when once again this most random of dates arrived and Gai insisted to be present with a cake and a carefully wrapped gift, Tenzo couldn't help but feel surprise. Today was the very day in the calendar Tenzo insisted held no specific meaning whatsoever, but Gai was here anyway, handing him over his gifts while showing one of his most genuine, most heartfelt smiles. So, despite everything Tenzo couldn't help but to feel rather happy anyway. (Today's date wasn't special in the slightest but getting Gai's attention was. Tenzo decided that it couldn't be helped.)
The End