-CLOSE RELATIONSHIP OF TRUST AND RESPECT WITH THE CAPTAIN
To emphasize the long history relationship between Luffy and Sanji, I will start from the beginning when Luffy awoke Sanji, both had their idols who sacrificed a body member to save them.
Throughout history they have fought oftentimes together, creating a deeper bond:
Luffy and Sanji vs monster cow-fish
Luffy and Sanji vs Laphans
Luffy and Sanji vs Satori
Luffy and Sanji vs Wapol
See when Sanji was portrayed alongside Kid and Law’s Vice Captains.
Some parallels:
-HOW LUFFY/SANJI RELATIONSHIP DEVELOPED IN WHOLE CAKE ISLAND
People often say that Sanji “cheated” on Luffy and so he is not as trustworthy as a vice captain would be. But this is absurdly false, there were a number of events that involved the integrity of people Sanji likes, and Sanji orchestrated a betrayal of Luffy just to protect the people he loves, like Zeff and the Mugiwaras, not to mention his hand of cook that could be blown up.
Contrary to what some think, Whole Cake Island has developed the deep relationship between Luffy and Sanji.
In this bow, Sanji was the only Mugiwara that Luffy says could not be king of the pirates without him:
Both also always trusted each other, at the meeting point for example, this in my opinion is an excellent form of relationship between Captain and Vice Captain.
Finally, Luffy and Sanji together repel the attack of a powerful Yonko.
Looking at all this, there is no way that Luffy and Sanji do not have a great relationship of Captain and Vice Captain, after all these interactions of trust and respect for each other.
Luffy has 2 right-hand men. These 2 are the pillars of the crew and the wings that make Luffy fly.
*Theory by Chaves