Razor never really knew when he was borned. His earliest memory had been that of Wolvendom, surrounded by his lupical. It was only when Varka found him and brought him to Mondstadt that he was introduced to the concept of birthdays.
His real birthday was never known, lost to the wind and time. However, that did not mean that he did not have one. In the end, Varka declared the day that he first found Razor in the woods would be Razor's birthday.
(Razor did not argue nor agree to it, but it was also because he was too busy eating Sticky Honey Roast to do so.)
Klee had been delighted at learning when his birthday was and promised to always remember it (only because Razor kept forgetting until a few years later). She would prepare a gift for him the month before, hiding away in her room to make it a secret (even if everyone including Razor knew) before searching him out in Wolvendom on his birthday to give it to him. Razor cherished each an every one of those gifts (except for the one time Klee gifted him a bomb), and kept each of those gifts in a wooden chest.
He loved pulling those precious gifts out on lonely nights, either to look at them or to feel them with his fingers to warm his heart.
As time went on, his circle of friends grew. He liked that his friends did not care that he disliked speaking due to the way he spoke. He liked that his friends accepted him even when his family was made of wolves instead of humans. He liked that his friends wanted him for himself, not for his strength, his Vision, or his relation to the Knights of Favonius.
Then his circle of friends expanded to include the Traveller, a famous hero, and suddenly people wanted to talk to him. Razor understandably retreated to Wolvendom and he was glad that his friends were willing to hang out with him there. The Traveller had been apologetic, willing to break off the friendship for his sake but Razor had refused, adamant to keep the friendship that he had made with them.
On his first birthday, the Traveller had sent him a parcel containing a handwritten letter and a box of dried meat. No one had sent him a letter before, no one expected him to know how to read. And they were right, however, this setback was not one that will stop him.. He had rushed off to Lisa, badgering her to read it for him and finally, help him write a reply back.
He told his friends about the Traveller's letter and how he was happy to receive something that contained a personal touch of their emotions even if he did not know how to read it well.
His other friends wrote him letters after that and Razor would go to Lisa each time he had trouble reading it and writing a reply. As time went on, Razor's understanding of the language improved and with it, came his confidence to speak more.
In a blink of an eye, a year had passed and it was his birthday again. However, this time, he wanted to be the one to send the Traveller a letter before they did. He sat down in the library, placing the writing materials on the table in front of him and he began to write.
It's been some time since I last smelled you. Missed you, a bit.
I got stronger. I talked more, and ate a lot of meat.
Did you eat good food, too?
I like this meat, for you. Together, we get stronger.
Maybe next year, he will be able to write a longer letter!