This 'What If?' fight prediction is based on an idea I had for an animation when I was 15, having just read the conclusion Enies Lobby. I was never able to complete it due to sickness, so let's see where this goes! Note - this takes place before the time skip so no Haki tricks.
Narrator: A sole figure silently trudged throughout the vast expanses of the Alabastian desert, it's plains spreading into the horizon and forever beyond. Up close you could see that it was a smartly dressed man, who wore a double-breasted black suit only for the jacket to be used as a makeshift shade, that he held over his head. Without the jacket on, it revealed an oceanic blue buttoned up shirt and black tie underneath, soaked with sweat from the relentless heat -
Sanji: (shouting into the sky) WHAT ARE YOU TRYING TO MAKE THIS SOUND LIKE!? A fan fiction by some 13 year old girl??
Narrator: (A 13 year old-?? *cough* You're right, I'll keep going) - The ruins of a civilisation long since lost were scattered amongst the dunes, only the highest floors of the ancient buildings made their way to the surface now as they continued their millennia long sink.
Sanji: Shit! The worst part isn't the heat, it's the fact I have no idea how I got here, and where 'here' even is!
Narrator: (flashback) Sanji finds himself lying face down in the sand, fully dressed but no idea where he is. Struggling to pick himself up, he flops over only for the sun to assault his eyes. Finally standing to his feet, he takes off his jacket to use as make-shift shade. (end flashback)
Sanji: That was a pretty harsh thing to do, dropping me into a desert. Is this going anywhere?!
Narrator: (Shh-shh-shh... I got this. Just keep walking.) Reluctantly, the young man continued his trek further into the desert. However, it wasn't too long before he discovered he was no longer alone...
Sanji: Oi oi, is that somebody else in the distance?? HEY!! You there! Where are we?
Narrator: (I wouldn't do that if I were you.)
???: YOU BASTARD!!
Narrator: Unbeknownst to Sanji, the looming figure he saw in the distance was not friendly at all. As he continued to walk cautiously nearer, the shade finally lifted from the intimidating man's face.
Sanji: Crocodile?! But I thought we...?
Crocodile: You... you're that Mr. Prince that made a fool of me back at my casino, Rain Dinners!!
Sanji: Umm, well... yes that was me- !!
Crocodile: HOW DARE YOU!! What did you do to bring me out here!!
Narrator: Crocodile immediately launches forward, his lower body transformed into sand, and lunged at Sanji with his golden hook; the later only barely dodging it's point.
Sanji: (mid-air, arms and legs spread back in surprise) I haven't done anything, you shitty bastard!
Crocodile: Then who else is it!? All I see is you and me, and it surely isn't me!! Desert Spada!
Narrator: Forming his right hand into a miniature, swirling maelstrom of sand, he struck the ground and launched a powerful torpedo towards the cook, leaving the ground behind split in two. Yelling in terror, Sanji rolls out of the way yet again.
Sanji: (coming to his feet, pointing at the sky) This is all of your fault!! What kind of shitty bastard forces two people to fight!!
Narrator: (A writer, by the way watch out from behind.) Sanji turns around slowly, hesitant to see what he knew was coming.
Crocodile: Who the hell are you talking to, you're dealing with me right now remember?!
Sanji: (becoming serious) Oh for the love of god...
Crocodile: Barchan..... (Crocodile's right arm turns into a trailing blade of sand...)
Sanji: Mouton Shot!
Narrator: Just as Crocodile was about to strike Sanji, the cook instead directed his kick into the ground between them, launching a large quantity of sand into the air and obscuring both combatants' vision. Solidifying himself, Crocodile quickly swept his arm to blow away the sand, only to discover Sanji had disappeared.
Crocodile: (frustrated) Where are you? Coward!!
Narrator: Behind a nearby ruin, Sanji was left hiding in the shade. Peering over the corner, he notices Crocodile had already guessed where he could be, as the ex-Shichibukai was now decimating any cover he could see.
Sanji: God damn, and they created such good shade too... but what am I meant to do? The guy is downright made of sand, I can't hit that. Luffy used water... gahh what am I saying?! There's no water here!! How would I even use it?! (imagines himself as Mizu Sanji)
Narrator: Suddenly, from behind...
Crocodile: Found you, worm! (jumping into the air, his legs turning into sand to float) Sables...
Sanji: Shit-!! (time slows down as he goes to move)
Narrator: Firing a condensed ball of sand and wind, it rocketed towards the ruins Sanji was hiding behind. Striking the base of the building, the area was immediately engulfed within a large shockwave, instantly decimating the ruins. Eventually, the destruction settles down leaving Crocodile floating amongst rubble. From above, Sanji's black jacket falls down in tatters, raining over the ex-Shichibukai.
Crocodile: (laughing) There's nothing left of the sorry bastard, now with him dead will I be returned?
???: (from behind) Dead?
Narrator: Turning around in disbelief, Sanji had appeared directly behind him, having jumped up from the ground despite being seriously injured. The cook held his arms up to his face, and only then did Crocodile realise his right leg was ablaze.
Crocodile: What are you-?
Sanji: Don't go killing me off so quickly you shitty sand-man! Diable Jambe: Collier Shoot!
Narrator: Spinning around and striking Crocodile in the neck, rather than passing through his intangible body, Sanji's cowardly surprise attack instead sent Crocodile flying backwards. (Sanji: WHAT DO YOU MEAN, COWARDLY?!) The ex-Shichibukai reformed his legs, and landed heavily onto the ground.
Crocodile: That Mr. Prince, how did he hit me... (reaches up and touches where he was stuck) What is this, glass?!
Narrator: The section near Crocodile's collarbone was now crystallised, the glass-like material cracking apart.
Sanji: (landing onto the ground several meters away) I couldn't figure out how to hit you, as before now the only weakness I know you to have is water. But, then I remembered something. (pointing towards Crocodile) Glass is simply sand heated to extreme temperatures! And low-quality sand like what your body is made of will only produce brittle materials.
Crocodile: You bastard...
Sanji: Prepare yourself, I'm coming for you Mr. Zero! (lunges forward at high speed)
Crocodile: Hell-!! Desert la Spada!!!
Narrator: Forming several large blades of solid sand, Crocodile launched them all at the cook. Sanji managed to narrowly dodge the first two, only for the third to impact directly onto his torso, ripping his shirt open and cutting into the flesh beneath.
Crocodile: (shouting) That should slow you down!
Sanji: (growling) Don't... you count on it! Diable Jambe... (jumping ahead again, Sanji lands in front of Crocodile while crouching) ...Frit Assorti!!!
Narrator: Kicking upwards at Crocodile, striking him squarely in the chest three times, the large man was sent flying into the sky, coughing up blood while his torso slowly crystallised from the intense heat.
Sanji: Shut up, you!! (Narrator: W-what?) This is my story now!!
Narrator (Sanji): Jumping into the air, chasing after his overwhelmed foe, the devilishly handsome man (who happens to be the best cook on the Grand Line) delivers a powerful vertical kick to Crocodile, shattering the front of his already crystallised torso!
Sanji: Diable Jambe: Anti-Manner Kick Course!!! (Narrator (Original): You can't just hijack this story!!) Watch me you shitty observer.
Crocodile: I don't know who you've been talking to this entire time, BUT IT ENDS HERE AND NOW! (reaches out and grabs Sanji's right leg with his right hand) Desert Encierro!!
Narrator (Original): (See what you've gotten yourself into!?) Draining the moisture from Sanji's right leg, causing it to mummify, the young man screamed in agony as his leg was rendered unusable. Sensing victory, Crocodile raised his hook prosthesis high into the air, laughing manically.
Crocodile: Any last words, Prince?!
Sanji: (coughing) Yeah... that pause to gloat, is going to cost you!!
Narrator (Original): Reaching out with his left hand, Sanji grabbed Crocodile's crystallised collar bone and pulled himself above the sand-man, quickly kicking him a short distance downwards. Not taking a break, Sanji immediately began spinning at high speed as his body started to fall. Just as he was about to make contact with Crocodile, Sanji broke his momentum by coming down onto Crocodile's abdomen with his left leg, now ignited.
Sanji: Diable Jambe: CONCASSE!!
Narrator (Original): The final blow struck, Crocodile was sent flying into the sand below, the impact caused a large crater to form, the displaced sand flew outwards in all directions. Landing nearby, Sanji collapsed from exhaustion.
Narrator (Sanji): And it was all thanks to me, damn the only way I could be happier is if Nami-swan were here to witness my shitty victory!
Narrator (Original): Yes well, too bad none of this actually happened.
Narrator (Original): Yeah, you didn't actually think you could beat one of the Shichibukai that easily did you? Maybe post time-skip but...
Sanji: What time-skip!?
Narrator (Original): What? Oh don't worry. You have a great time, I promise.
Sanji: But I-!
Narrator (Original): AWAKEN!