This is when Bluejam and his crew capture Ace and Luffy during the burning of the Gray Terminal.
(Witch AU)
Bluejam sneered, the little brat squirmed beneath him, snarling and angry, but also fearful. He refused to let Ace pull another trick, that trick where he had knocked out all his men. He began to pull the trigger, but a hand grabbed his, and shoved his away.
He looked up, a snarl on his lips, and froze.
Piercing dark red eyes met his own, and everything he had drained away, replaced by absolute terror. He trousers felt warm and damp, and his legs shook. A delicate hand, or seemingly delicate, crushed his hand, and shoved him off the brat.
Bluejam screamed, cradling his hand as he stumbled back, trying to put space between him and the woman before him.
Strawberry blonde hair, red eyes, and a cowboy hat with a hibiscus flower tucked on to it struck something in him. He recognised the look, but for the life of him he couldn't recall who they were.
He was too busy trying to fight back the pain. All he could feel was his broken bones, crushed within his hand.
"Keep your fucking hands off my kid, you son of a bitch."
.::.
Dadan had ran, her heart racing. Bluejam was about the pull the trigger with Ace pinned in place beneath him. Ace wouldn't survive, and god he was Dadan's kid at this point. She had raised him since he was a baby, small and soft and so happy until Garp had told him the truth-
She couldn't lose Ace.
A shadowy figure was instantly before Bluejam though, long before Dadan could get there. The woman crushed Bluejam's hand and threw him back. The shadows melted off the woman, and a vaguely familiar strawberry blond stood before them all.
Hibiscus Rouge, the pirate thief herself stood before them.
Ace's mother.
Who was pissed.
Dadan froze in place when their eyes met, all her danger senses going off. She barely fought off the urge to retreat, shivering beneath those piercing eyes.
.::.
Portgas D. Rouge had shattered the hand holding the gun, and shoved the piece of trash back. He was sobbing, scurrying back like the waste of space of was. Dadan, the bandit, had frozen in place when their eyes met. There was fear in her eyes, of Rouge, but also fear for Ace, which was slowly ebbing away.
Rouge smiled, and turned around to pull Ace into her arms. Ace let out a startled noise, but Rouge hugged him tight.
"Hello, Ace."
"H-H-Hi-HIBISCUS ROUGE!" Dadan shrieked.
"W-What?" the trash gasped.
Ace froze, baffled. His brow furrowed, and he clung to her. "Wait... You're the shadow lady... Why do you look like my mum? You... What you just said..."
Rouge smoothed his hair back. "My name is Portgas D. Rouge. I'm your mother, Ace."
"But... I..." Ace whimpered, shaking beneath her hands. "I... I'm so sorry, Mum! I... I got you killed and- I don't understand how you're here!"
"No, Ace. No," Rouge said, shaking her head. "It was the World Government and the Marines that killed me. As to why I'm here? Well, I'm a Portgas Witch, and our ancestors are always connected together, Ace. I'll explain our history to you in time, but for now you're getting really tired from my using your magic."
"Mum-" Ace began, wide eyed, before glancing over her shoulder, right at the pathetic waste of a pirate. "I-"
"I'm glad I got to finally help you," Rouge grinned, pressing a kiss to Ace's forehead, and oh god, it felt so good, good to hold Ace in her arms properly.
The last thing she felt as she left this world was Ace's tiny form, so small and delicate, in her arms. Cradled gently, and safe. So safe. He was still small, and soft even now, so she clutched him tighter. Their magic was weakening, Ace was still too young to use spells, and Rouge had forced herself through into the living world. Ace was growing tired, his eyes heavy, so she carefully handed him to Dadan, who surprisingly took him into her arms gently.
"We're going to have to talk one day, you and I, because I know the things you've said, and many of those things I dislike," Rouge said, and Dadan whimpered. "Be thankful, you've kept my son alive all these years, so you get to live. Now take Ace and Luffy, and get going."
She turned on her heel, and began to approach her prey. Because that was what this guy was, prey, to torment, to tear apart, piece by piece, for touching her son. Bluejam hurt Ace, tore Sabo away, forced Ace to work then tried to steal off him and murder him.
"So, Bluejam was it? I've never heard of you. But such is the trash that litters the street," Rouge chuckled mockingly. "You don't touch a head witch. You don't try to kill them, or their ancestors will drag you down into the deepest of Hells."
"I-I-"
"You, you," Rouge drawled, ignoring the bandit's whimpers of terror. "The Nico family taught me quite a bit of their special Death magic. Of course, it belongs to the Nico family, while the elements belong to mine. But, I suppose I can bring the ghosts of Hell upon you."
He fired his gun, and the bullet went right through her. Rouge laughed, stalking forward, and tapped into the last of Ace's magic. Ace would be exhausted after this, but he'd sleep and recover, just as all witches did.
The ghosts of hell began clawing their way out of the ground, sinking their nails deep into Bluejam. Bluejam screamed, firing his gun, but Rouge ignored the bullets. They went through her body, passing by harmlessly.
"I'm a ghost of the Portgas family," Rouge laughed. "You can't kill me. I'm already dead."
He was dragged through the mud screaming.
"Rest in peace," Rouge mocked.
She turned around, walking away, and with a flick of her hand, Rouge returned back to the afterlife of her ancestors.
So Rouge's magic is connected to Ace's. So whenever she uses her magic, it is actually his she is using. Hope that explains the magical system for those two. She can no longer tap into hers' because she died.