I think Usopp is Luffy best friend. I don't think Usopp really helps Luffy grow as a person or leader. Luffy definitely helps Usopp grow.
I enjoy all of their best friend moments. The most recent one is that Luffy is undefeated in Sumo wrestling amongst the crew, yet his only opponent was Usopp. That means the two of them decided to have a Sumo wrestling tournament, but most likely no one else wanted to join.
I enjoy all of their best friend moments. The most recent one is that Luffy is undefeated in Sumo wrestling amongst the crew, yet his only opponent was Usopp. That means the two of them decided to have a Sumo wrestling tournament, but most likely no one else wanted to join.