Ace started it. After they all finished pretending to be bad guys and were digging in to the food, the fireman had declared that he was leaving. Apparently, he was looking for someone.

Locks didn't take it well. Apparently, she had had spent three years babysitting Luffy by herself, plus the time since Luffy had set out to sea. Ace had abandoned her to the hyperactive rubber boy once; he wasn't going to do it again. Not if the resident dragon had anything to say about it. In fact, she had explicitly stated that she would roast him if he tried to go.

Ace had, of course, pointed out that he was made of fire, and therefore fireproof and unroastable. Locks had informed him that she was half-Thunder tribe and had repeated that if he didn't pull his weight with Luffy, she would roast him. Ace completely missed the point that she had made, and had the temerity to answer 'Yes' when asked if he really thought he was going to be able to leave.

That was, perhaps, not the best response to give an increasingly cross female dragon. Hell hath no fury, and all that. Locks had then proceeded to prove that she damn well perfectly capable of roasting any fool (for Ace was certainly a fool) she liked, made of fire or not. For what goes with thunder, but lightning, and lightning was quite good at roasting foolish older brothers.

So the crew all sat very quietly on the sand, hoping not to get involved, watching as Ace fled in terror from the angry lightning-beam-breathing dragon.

The scariest part, Usopp sincerely believed, was not the moment when Ace's entire skeleton was showing, but when Nami quietly whispered to him, "I'm going to be able to do that, right Usopp?"

oOo

'Fire-fist' Portgas D. Ace, Second Division Commander of the Whitebeard Pirates . . . lay twitching on the ground, looking very scorched, and quite thoroughly roasted. A victorious dragon stood over him, sparks crackling around her nostril with each breath.

Then Locks returned to her human form and said that, since this person Ace had been looking for had been spotted in Drum (where Luffy demolished a dictator) and here in Alabasta (where Luffy was going to demolish a would-be dictator), wouldn't it make sense that third time would be the charm, and that this person would be found wherever Luffy went next?

Ace's fervent agreement with this statement probably had a lot to do with the crackling around Locks' fist.

And so, Ace changed his plans and decided to help them get rid of Crocodile. And babysit Luffy. Can't forget that part.

oOo

The rest of the journey to Yuba (where Vivi said the rebel army she wanted to stop was stationed) was filled with Ace complaining how his little sister used to be a lot more respectful and obedient. Locks continuously and cheerfully reminded him that that was before she spent three years alone with Luffy keeping the idiot rubber boy from getting himself killed. Fire-fist eventually (reluctantly) conceded the point, after which both he and Locks proceeded to terrify the crew with tales of their captain being eaten by crocodiles and wrestling with monkeys and . . .

oooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo

Sorry for the late update. And while Ace might be a badass worth 550 million beri, he wouldn't defend himself anything that might seriously hurt his sister, and angry females can be quite vindictive.