I don't really know where the idea came from, just 1 am randomness. Even though I didn't watch One Piece in a while, this idea just seemed to fit. And some things may be over exaggerated or not 100 percent truth, so I apologize for that. Haven't been in an OP modd in a while so I'm a little rusty. Anyway, with that being said, I hope you enjoy!
Seven Deadly Sins
Envy
Usopp had always been envious of his crewmates. They all had something that he lacked greatly: bravery. All of them seemed no fear absolutely nothing, or if they did, they never showed it. Even Chopper seemed to be rarely intimidated. Sure, they all had their weaknesses, but they had enough bravery to overcome their weaknesses and fears and probably extra, unlike Usopp. He barely had enough for himself.
During battles, he was never the first to step up and declare a fight. Rarely did he alone go to challenge someone. Only if the others were doing it, like Luffy or Zoro or Sanji, would he fight along side with them. Even while he fought, most of his attacks were used as diversions for him to run away or hide. He hated fighting hand on hand. He felt safer hiding amongst other things or people and always felt a strong advantage in surprise attacks. He also couldn't say that he wasn't a bit envious of his opponents as well, for they could fight with both amazing skills and endless bravery, two things he wished he had.
Usopp often wondered how they all did it, and he was jealous each time. When Zoro fought Mihawk, he showed no signs of backing down until he couldn't move a single muscle in his body. As strong as Arlong was, Luffy kept on pushing and fighting until he won. Even when Nami was sick, Sanji wasted to time in volunteering to take her up the dangerous mountain climb. He always envied their seemingly natural bravery. They all worry for him, worry that he might forget that even though he lacked in bravery, he made up for it with everything else he was.
Greed
Everyone on the crew always knew Nami was greedy. At first, they saw no real explanation to it and saw it as one of her traits. After all, Luffy and Zoro didn't mind too much when she took the treasure from the pirates they defeated. However, when Nami went as far as stealing the ship and leaving them stranded at Baratie, they knew she had gone too far. They soon learned at Arlong Park that it wasn't really her fault; she was forced to be greedy.
Even after Luffy defeated Arlong, her greediness did not go away. It decreased all right, but it was certainly still there. They were still pushing into battle just for the money and usually had to ask her to borrow, even though the interest rates where horrible. She still kept all the money in check, keeping some in a secret hiding spot. They never really argued with her, because it was, after all, a part of her. They learn to accept it, just as they do with all of their nakama.
That's not to say, however, that they have their fears. Luffy, Zoro, Usopp, and Sanji sometimes worry that she might be consumed by greed for one reason or another just as she was so many years ago. When Robin and Chopper heard of the story, they also had their mild worry. They worry that she might be corrupted by greed again and betray them, just like before.
Pride
Zoro was very prideful in his swordsman skills, sometimes a little too much so. Everyone knows he's one of the best, almost as good as Mihawk. With a little more practice, he could easily pass him. He knows this too.
He makes sure to practice daily and fight regularly, even if just sparring. He reminds himself why he does it. He promises himself to not let down Kuina and keeps their promise. He always takes pride in what he accomplished, enough for both of them, because he knew if Kuina was still around, she would take as much pride in her skills just as he would. So, he has to do it for the both of them and make sure he's extra prideful when he shows off a new move.
They don't really understand his background story, only Luffy and Nami know some of it. He likes to keep it secret and just let them think he sometimes can have a little too much pride. Though he doesn't say, most them can try to understand. Even though they know they can't fully, they still try. But they still worry that he might take pride in things he really shouldn't, but does it anyway just in case his friend might've.
Gluttony
Luffy could literally eat a whole horse, if not more. He loves the taste of meat, raw, cooked or burnt. Just about anything that's eatable tastes wonderful in his mouth and it often forces Sanji to cook extra just to satisfy their captain. But food isn't the only thing he hungers for.
It rarely happens, but during battles he can feel it. Sometimes, when he gets over emotional and his devil fruit kicks in, he can feel that hunger in the pit of his stomach. Just like when he fought Arlong, he hungered for more power and more strength to beat him to a bloody pulp, and then some. He could feel himself lose control to the Devil's Power lying inside of him. The power that wanted to give him the extra power to fight harder. He doesn't realize when he finally finishes an opponent and wants to hit him some more just to remind them never to miss with his nakama.
It doesn't happen that much, but it's still there. Nami noticed it when he fought Arlong and she couldn't help but feel it was her fault that he would be consumed by that hunger. The others remind her that everyone has a part in the blame. And though he doesn't know it, they all worry for their fun loving captain and pray that he stays the way he is.
Wrath
Chopper hates a lot of things, but he doesn't show it. People like him as a little, friendly reindeer, so that's what he would stay just to stay with his only friends. He secretly hates pirates, the villagers, sickness, other reindeer and so many more. His hate soon turned into anger towards these things, but he still doesn't show it.
As he grew up, he was never accepted. He was angered by his so called herd that left him behind because of his different colored nose. Once he ate the Hito Hito fruit, he hoped that maybe, the humans would accept him, and he only got angrier when he wasn't. When he finally found his only friend, he is soon thrown out again just to not watch him die. He tries to hide the fact that he's angry at Dr. Hiriluk for not telling him, angry at the Jolly Rancher for not curing the doctor's disease, angry at sickness in general just for existing, and angry at the mushroom he found that didn't help his only friend. Even with all of the anger he had, he lived on with a smile on face while living with Dr. Kureha. The only reason he stayed happy was because he knew that Dr. Hiriluk would never want to see anything else on that face.
When he joins the crew, the smile isn't always fake. He finally remembered what it felt like to have a friend and to feel accepted. But even with all of that, the anger didn't go away and they knew that. Even when he had that big smile on his face, they worried that all the anger he was suppressing would come out the wrong way.
Sloth
Robin labors an intense hatred for the world and doesn't know why she should be thankful for it. All the world ever did was rob her of her childhood because she ate a fruit that the world produced. It was because of that one incident that she couldn't grow up like a normal child. No, she was forced into hiding because at the age of eight, she had a 79 million belli bounty, all because some marines that attacked her hometown made up a lie of her sinking six Navy ships just to cover up the nasty truth.
She had lost the most important people in life, her mother and Saulo, because of the twisted events that the world had plagued her with. Maybe she should've blamed the marines for attacking Ohara, or maybe she should've blamed her mother for leaving in the first place, but at age eight, she blamed the world for playing such a cruel prank on her. She learned over the years that even the people who befriended her eventually tried to turn her in, either because of fear or greed. Either way, she learned what the world really thought of her. The world thought of her as a sin, a sin that shouldn't live. The world taught her to never trust anyone, just stay with the strong and betray them when danger arose. The only thing that kept her sane through the years was knowing that some day, some how, she was going to find the True History.
They sometimes worried too much about her. They all came from twisted and cruel childhoods, some more than others, and they knew she was no exception. Even though they were initially worried when she joined they crew, they have more important things to worry about. Constantly, they worry if she still hates the world and wonder if she will ever realize that it's not the world, it's the people.
Lust
Anyone could tell that Sanji was a natural flirt. They thought it was harmless, just a way to charm ladies, but they never knew. They never knew that sometimes, he would lustful for some of the women he innocently flirted with. None of them knew exactly how or why he felt that way.
He had lived a childhood all alone. Before the pirates attacked, he never had anyone to play with. He would often hang around alone. After he was stranded on the island, things only got worse. With a dry mouth and empty stomach, he would talk to himself to make him feel less lonely. He would often think of family, and what would've happened if he was here with his. Love left him over the days as he drew the line on the ground. What he needed was love or a family, but it never came. And so whenever he felt with the ladies, he does it to rid himself of the loneliness he still has in the back of his head. He lusts for more and wants them to stay with him forever, just so he knows he'll never be alone again.
The crew had picked up on this a while back, but they never said anything. They never let on that they knew what was wrong. They figured he was Sanji and everything would turn out okay in the end. But, whenever they saw him looking at a lady, they worried that she might break his heart and leave him all alone again. Or even worse, she might make him forget his friends that will never leave him to the loneliness.