I'm, for the most part, indifferent about LuNa, but I've noticed a poor portrayal of Sanji in most of those stories. One-dimensional, incredibly jealous, intent on killing Luffy, and somehow ignoring Nami in the whole process. Not to mention Robin.
I don't know if he'd react like this, or like that, or whatever you think he'd do. It's just to prove a point- that Sanji isn't shallow. He cares about all of them. He really does.
If anyone on the crew were to become romantically involved with a woman, one of the last people anyone would suspect was Luffy.
Luffy was about as sexually active as a piece of bread that had gone stale in the pantry.
So the entire crew was stunned when Nami finally decided to break the news by giving Luffy a showy kiss at the dinner table. Luffy didn't appear to be affected by his new relationship much. He had simply swatted Nami away and continued stuffing his face with food, seemingly oblivious to everyone's individual reactions.
Still, despite Zoro's snorts of doubt and Usopp's shrieking of terror, Nami insisted that she and Luffy were... together. "Couple" or "boyfriend" or "romance" didn't exactly fit them. Because, Luffy was still Luffy and Nami was still Nami; she still smacked him around and yelled at everyone, but it was just the way she smiled at him or ruffled his hair that set the fact that she and Luffy were together.
Luffy had no input on the matter, although he did nod a few times when questioned. If more than anything, he was more concerned with cramming as many pieces of grilled chicken in his hamster-like cheeks.
Zoro was completely indifferent and didn't give a damn, Brook promised to write a love song for the two (Nami strongly objected to this), Franky congratulated the two while wiping tears away from his eyes, Usopp and Chopper were rather shocked but quickly accepted the news, and Robin's blank, polite smile hardly wavered during the entire ordeal. Sanji probably took the news the worst.
Sanji didn't say anything, but one could have felt the anger rolling off of him if anyone had paid attention to the strangely silent cook. Robin, on the other hand, found it odd that Sanji hadn't said a single word since Nami had kissed Luffy much less went off on a rampage.
"Cook-san?" Robin found Sanji in the observation deck after dinner, quietly watching the ocean from the high windows. Nami and Luffy were sitting together underneath the tangerine trees, and even from up there, Robin and Sanji could hear Nami scolding Luffy about something and Luffy strongly denying whatever he had done. Nothing had changed, but they could still tell. They were together.
"Hello, Robin-chan." Sanji quietly said, taking deep inhalations from his cigarette. Robin stood beside him and observed a flock of gulls skimming over the waves.
"I'm surprised you haven't said anything."
Sanji exhaled, smoke curling against the window.
"Cook-san, we all know you don't approve of Captain-san and Nami-chan's relationship." Robin said. Sanji still said nothing and concentrated on his cigarette.
"So what did you expect me to do?" Sanji asked stiffly.
"Who knows?" Robin shrugged, her faint smile never faltering. Sanji rested his forehead against the cool glass. He closed his eyes and listened to Nami laughing at something Luffy said then quickly saying something sharply to him.
"I'm not going to try to break them up, or anything shitty like that if anyone thinks I would." Sanji finally said after some moments of silence. Robin nodded.
"Because it's not like I'd beat the crap out of Luffy just for... Nami chose him, after all." Sanji continued. "He's still an idiot. Yeah, I do think Nami could have chosen someone better-"
"Like you." Robin guessed. Sanji took a deep breath, his cigarette forgotten between his fingers.
"No." Sanji pressed his head against the glass.
"But you love her." Robin pressed on.
"Luffy, don't pluck the leaves from the trees!" Nami's voice carried up through the wind.
"But they smell funny!"
"Uh... but you're hurting the trees."
"Eh?! They can feel?!"
"Yeah! Jeez, Luffy, can't you hear them crying from the pain?"
"Ah! Ah! I'm sorry, tangerine trees! I'll put your leaves back!"
"One wouldn't think that they're a couple." Robin chuckled, watching the two beneath the trees.
"I would have never expected Luffy, of all people, to start a romance. If you can call it that." Sanji scowled, watching Luffy attempting to stick the plucked leaves back on the branches while Nami facepalmed and smiled behind her hand.
"People surprise people all the time. You could think that you know someone very well, but in the end, well, you get the idea."
"Why would Nami-san choose that moron, though?"
"She can be as unpredictable as Captain-san at times." Robin chuckled.
"Not Nami-san!"
"From what I've learned from my experiences, you can never expect the obvious from the people around you." Robin softly said, looking at Sanji from the corner of her eyes. "You have to learn to brace yourself for the worst, or the best. Whatever comes your way, you always have to be prepared."
Sanji bit his lip and said nothing for a long moment. He briefly dwelled upon possible explanations as to why hardly anything fazed Robin, toying with a few ideas.
"Sometimes, I did pretend that we could have had something." Sanji finally said. "I pretended that Nami-san loved me back." Sanji sadly looked at Robin. "Did you ever love anyone, Robin-chan?"
"No. I never had time to think of such arbitrary matters like love." Robin said without any regret. "I don't mind Nami-chan and Captain-san's relationship, either. I would have liked to think that we were all just nakama, but I was apparently wrong." She shrugged nonchalantly.
"Love... as soothing as a river of silk, yet burns at the heart like the spiciest pepper. I can never get enough of it." Sanji smiled crookedly.
"Cook-san, do you feel any anger towards them whatsoever?" Robin's eyes took on a hard look. Sanji hesitated. He knew better than to lie in front of Robin.
"Not anymore." Sanji slowly said. "Yeah, I wish that I was in Luffy's place, but..."
Robin patiently waited for Sanji to find the right words.
"As long as Nami-san is happy, then I'm happy." Sanji finally said. "Even if it means her being with the shitty gomu, I'm fine with that."
"You will find someone eventually. I'm sure of it." Robin smiled.
"Thank you, Robin-chan." Sanji's expression lightened up considerably. He began to rock back and forth on his heels. "Maybe- if, uh, well-"
"You're all my nakama. Nothing more." Robin said with a hint of amusement as she left the observation deck, leaving Sanji standing by the window. He dropped his cigarette, which had slowly burned out. The gulls had disappeared over the horizon and the stars were beginning to fade in. Sanji sighed and watched Luffy run off to play with Chopper while Nami kicked Brook, who had no doubt asked for her panties. Zoro shouted at Nami for being so noisy which sparked a heated argument between them. Usopp and Franky were at the front of the ship, tinkering with their latest project.
Nami punched Zoro one last time over the head before walking away to sit beside Robin. Robin looked up at Sanji and smiled knowingly. Sanji waved back and leaned on the windowsill, watching the crew from above.
Even though Nami and Luffy were together, nothing seemed to have changed. But in a way, everything did.
But it wasn't like it was bad, or anything.