LuNa

Canon
Luffy is the capitain and Nami is the navigator of the StrawHats crew. Nami is one of the Luffy's older nakama. She has been there since the crew was in the East Blue. She can be considered as the third or fifth member of the tripulation.

Luffy and Nami have a trust relationship, which can be seen since the first episodes, where Luffy leaves his treasure (his hat) on Nami's hands without hesitating; or that Nami is pretty sure that Luffy will help her in any situation she's in.

FIRST ARCS: Buggy, Capitain Kuro, Baratie Restaurant.
On the Buggy arc, Luffy asks Nami to join him, and she accepts only to have a way out of Buggy's hands. She ends up "joining" Buggy's crew for a few minutes, but later she helps Luffy and Zoro. Nami gets impressed by the fact that Luffy consideres his hat a tresure, and that he gets so mad by Buggy ripping it, so she offers him to repair the hat.

In the Capitain Kuro, Nami starts to understand Luffy's perception of "nakama", that is totally different from the pirates she has known.

Nami and Luffy do not have many interactions in the Baratie Restaurant Arc. Nami steals the Going Merry, and even though what Yosaku and Johny tell Luffy, he trusts Nami until the end, saying that there must be a reason for that, and sending the rest of the crew to bring her back, while he helps out in the Baratie.

Arlong Park Arc
Nami goes back to her village, and the StrawHats go after her, ignoring the fact that she does not want them to follow her or to even be in the village.

Luffy wants his navigator back, but he waits patiently, and shows that he does not care about her past, he only cares about the present.

After Nami gets so mad at Arlog for stealing the money she was reuniting, she finally, after so many years, asks for help, to Luffy. Who says "Of course I will", letting his hat on her head.

He beats Arlong, mad about how he made Nami cry.