We know Oda stated that Sanji and Zoro are Luffy's 2 Wings but that only apply for his crew.
he has has many duos around hims and are about armament/toughness of the body/strong attack power and observation/sharpness of the mind / speed.
he has has many duos around hims and are about armament/toughness of the body/strong attack power and observation/sharpness of the mind / speed.
- the first Duo is obviously is in his crew Zoro for the armament and strong attack and Sanji for the observation and speed
- the second Duo are his rivals : Kid and Law Kid obviously has tough body and can use metal , and Law is a strategist with sharp mind . Don't be surprised when it gets revealed that that Law is CoO specialist and Kid a CoA specialist.
- the third Duo is his friend the Kings and ancient weapons Shirahoshi and Momo is obviously is the commander of Pluton that stand for strong attack power. Shirahoshi commands all Sea King which would be useful for observation and gathering intelligence.
- the fourth Duo. sworn brothers duo Sabo of the revos obviously is an armament haki monster with fire power. Ace is dead but i think Koby of the marines will join Sabo as a brother and his an observation monster.
- the grand Fleet Duo. Bartolomeo who has the barrier DF which stands for toughness and Cavandish who stands for speed , in his Hakuba form i think he will be an observation haki monster already hinted by the shape of his eyes.
- parents Duo i would say Garp as grandpa armament haki monster and his Dad would be an observation haki monster it is already hinted by Garp is just a fool , dragon as strategist, and someone who was able to not get captured for decades.