Navi rough sketch

Navi:

"I'm not sure who's fooling who here as I'm watching your decay"

Well, who doesn't know Navi, huh? Very talkative, sarcastic, smartass, friendly and coffee addict X3
Navi was born as a Guardian Fairy in the Lost Woods of Hyrule. She lived with her Kokiri for around 3 centuries, traveling through the whole continent. They got involved in many different incidents but they never played a major role during this time. Not like she did when she teamed up with Link. However, that wouldn't happen until many centuries later.
Her job as a Guardian finished when her Kokiri died, even though she's extremely good with magic and Humans' spells she could do little for her friend. When he died she isolated herself from the world and lived a solitary life for a couple of centuries. However, one day the Great Deku tree summoned and we all know what happened then.

Nave had a very good reason to leave Link the way she did. After they went back in Time Shalin, goddesses of Time, requested her to do something for her. She had to leave Link in order to revive the Great Deku tree. With all the pain in the world she left Link and that was the time when he went to Termina.
After he came back she went back with him and tried to explain the best she could her reasons, about Shalin and all that.

Every fairy is supposed to live forever, however, that doesn't mean they are immortal. Once a fairy reaches the 500 years most of them are asked if they want to be a Great Fairy. Most of the time that would mean they would live in a magical fountain aiding at as many people as they can but Navi didn't want that. She had lost at her dearest friend before and she wasn't gonna lose anymore of them in their war against the Pristine Army. She became a Great Fairy but she begged to the Great Deku to let her live as a Stray Fairy. He granted her wish as a recompense for all the sacrifice and loyalty she had showed to him.

Navi is the kind of person who would give you a hand and wouldn't stop bothering about it. She'll mock of your flaws and will not stop doing it unless you make her stop. She has spent a bit too much time among Humans so she's definitely not an innocent a pure forest spirit. In fact, she picks up many of the nasty habits of the Humans like being addicted to coffee, cigars, borrowing books and never returning, and making fun of people in cheesy plays.

The four arms is characteristic of the Great Fairies, in the beginning she had a pair of wings and only a pair of arms but she lost her wings and won 2 more arms when she became a Great Fairy.