This is set after episode 130, when Vivi decides that healing Nami would be the ship's 'fastest speed'. This is Luffy and Zoro centric, a bit more than usual. I made Usopp a bit serious here because I know he has that side to him, especially when his crew mates need him.
"Luffy-san scared me."
Usopp looked up from his fishing pole in surprise at the princess's sudden confession. Vivi had approached him minutes ago but she simply stood silently beside him and thus Usopp hadn't bothered her with small talk, not when so much was on the princess's mind. She now seemed ready to talk.
The sniper shifted and Vivi accepted the offer; she dropped beside him and leaned against the wooden bars.
"If I had asked to go to Alabaster, he would have gone. I could see it in his eyes, that he would have followed my decision, since it concerned my people. He might have hated me for it-you all would have-but he would have gone."
The waves gently lapped against Going Merry sending the ship in a soothing pattern of rocking back and forth. However, even the waves seemed to have little effect in calming the distressed princess.
"How? How could he have trusted me that much? What if I had chosen differently? What would have happened to Nami-san? What if I asked him to head straight to Alabaster? What if-"
"We would have saved Nami Vivi," Usopp interrupted, alarmed by the shake in his friend's questions. "Whatever you've decided, even if Luffy decided otherwise, we would have found a way to save Nami. If anyone, Zoro would have made sure."
"Zoro?" Vivi wiped her tears as she looked at the sniper. The swordsman, the ultimate embodiment of indifference and insanity, always seemed to hang back in discussions. Furthermore, Vivi had never sensed such a close bond between Mr. Bushido and Nami-san. "Are Mr. Bushido and Nami-san close?"
"Not in the way you're thinking but that's not what I meant. Zoro would have made sure for Luffy. If Nami died, Luffy would have been devastated, and we all know that." Usopp continued to explain the dynamics of their crew to the princess. "Where our next destination is, is always Luffy's decision. And as stubborn as Luffy can be, he's not selfish or irresponsible. He knows better than anybody that as Nami's captain, he is bound to her promise to you just as much as Nami is herself. And Luffy knows that if anything happened to Alabaster because he ignored your pleas and healed Nami instead, the guilt would destroy Nami just as much. So Luffy would have no other choice but to take care of Nami, and that would mean taking care of you. That would mean taking care of your problems first. But Zoro knows that that path would send Luffy to disaster. And so Zoro, being Zoro and Luffy's first mate would choose to take care of Nami to take care of you by saving Nami and saving your country and...er... You don't get it do you?"
Usopp grinned sheepishly as he scratched his head. A few moments passed in silence before the sniper found the right words.
"Okay, put it this way. If Nami takes care of you, and Luffy takes care of Nami," Usopp gestured to their left with his chin, and Vivi turned to her side, finding what the sniper was trying to show; a irritated swordsman who smacked his captain's head for almost falling overboard again. "Who takes care of Luffy?"