One Piece: I’m Mihawk’s Son

While the battle raged vividly on Onigashima, and the inhabitants of Wano looked on in wonder at the distant island, another battle unfolded in the eastern region of Onigashima. This battle involved four ladies and a single man.
CHAAA!!!
A hybrid woman, resembling a white tiger mixed with a human female, slashed forth, her attacks imbued in sacred white lightning and moving through the battlefield at ridiculous speeds.
"..."
The man she was fighting against remained nonchalant as he readied his golden spear to counter whatever she had to offer.
CLAAANGG!!
CLAANGG!!
The clash of their weapons produced sparks and destruction. Gion frowned when she realized the man had advanced Conqueror Haki imbued in his weapon. He was certainly not a pushover, not like she expected him to be.
"Admiral Shironeko, I don't appreciate your presence on this island," he spoke coldly, fully aware of her rank and designation. However, Gion was no different.
"A pity. I don't answer to you, Knights of God. Unless the Five Elders order me directly, nothing stops me from facing you right now. You may be acting at your own personal behest! Unless you get Sengoku or those five to call me, I'm going to stay involved!"
CLAAANGG!!
She clashed once more before retreating swiftly, opening her mouth to release a howling scream of white divine lightning.

Unlike normal lightning, Byakko's lighting could shock the enemy's spirit, making the man grit his teeth and evade the barrage of incoming white lightning. He technically disappeared and materialized somewhere else, but Gion had already seen that future. She was waiting there, katana in hand, and so was Hancock with her leg imbued in her pink love energy.

BOOOOMMMM!!!
Both Hancock's kick and Gion's sword sank the Knight of God deep into the collapsed ground as they clashed against the man's golden spear. Much to their shock, he didn't back down; instead, his smirk remained!
He swivelled his spear back and forth intending to impale Hancock first, but a kick from another lady deviated the strike.
BAAANGGG!!!!
Primrose's slender leg blasted the strike away, shocking him for the first time.
"Incredible display of Conqueror Haki, even more than your daughter... I'm impressed, Boa Primrose."
"Hancock, take care of Robin!" She ignored him and stepped forward together with Gion. They didn't even need to be having this fight; once Robin recovered, they could just flee, and Veyron would take care of the rest. But sadly, Robin was having a hard time.
On the ground, the woman of darkness was still spitting blood and was back to her base form, clueless as to why this was the case. There was no wound, but the pain was almost unbearable.
"Don't allow that spear to touch you; it has poison or something like that!" She warned her companions.
Hearing those words, the man smirked and disappeared from his spot, appearing far away with a guarding posture, walking back and forth. He didn't seem to be able to produce 'flashy' attacks, but his mastery of the spear, his strength, and tricks definitely placed him in their hearts as a genuine threat.
All he needed was one strike, and Robin was already panting in unbearable pain.
"Gion, who is this bastard?" Primrose asked; she never let him out of her gaze even once.
"I don't know much about the Knights of God. Only his appearance, name, and rank. Donquixote Cervantes, the 7th Knight," Gion clarified, her silhouette growing bulkier as she discarded her coat, remaining just in tight trousers as the white lightning continued to spark in her hybrid body.
"Is he strong?"
"Does he look weak to you...? All Knights of God are said to be around the same strength, so... we can assume this bastard is more or less as strong as Mihawk."
Primrose's eyebrows twitched; that alone already made him a pain in the arse.
"That woman is indeed very troublesome to deal with; she even murdered Leonidas... but I'd say I'm stronger in many other ways~" He boasted, earning their scowls.
Gion growled, "He has been moving oddly for a while now. His movement is not fast; he must have some means of teleportation or something like that."
"As long as Robin recovers, we can leave... darling, can you manage?" Primrose looked back at Robin, who was struggling to even stand up. If she had to describe the pain... it was as if the spear was perpetually being stabbed into her chest over and over and over...
"Done analyzing?" He laughed and spread his arms forth.

They prepared for whatever he was about to do, but instead of an outright offensive technique, everything around them started to change and become something completely different. They disappeared from the cold thunderstorm rain in Onigashima and popped up in a mysterious world, a complete grassland bereft of mountains. The bright sun blazed in the sky, almost blinding them with its shine.
"What the-" Primrose mumbled. It was ridiculous; she could even feel the heat of the sun and smell the freshness of the grass.
Instead of answering, he moved two of his fingers together.
BAAANGGG!!
Gion and Primrose gasped; their bodies crashed into one another with a mere gesture of his fingers!
Both of them fell to the ground, rubbing their foreheads and clueless as to what was going on. However, they had seen power like this in someone else's arsenal.
"Is that Veyron's power!?" Primrose didn't voice it out, but that looked a lot like his psychokinesis.
"It can't be!" Gion growled back and charged forth. She refused to believe she'd have to deal with someone with a power as troublesome as Veyron's. But it was all for nothing; her body moved on its own, crashing far away.
The man kept playing, waving his fingers back and forth and sending the two of them flying like ragdolls. Hancock and Robin were both visually stupefied by what was happening, but then... it dawned on them. They both regarded one another and then at Robin's 'wound,' and everything made sense.
"Mom, Gion... his power is illusions! Nothing of this is real!"
The man's amused countenance dropped.
Robin groaned and stood up before she took on her demonic form once again.
"You have some very strong illusions," she spat blood and smiled, still feeling the pain... but one way or another, it was receding bit by bit, as if a realization she imposed with her will. But someone with a weak will would definitely be unable to escape from this power.
"Thank you. So what if my trick has been given away? You're still feeling pain~ Illusions aren't only visual, a person's suggestion is also a form of illusion" He crated a butterfly flying around his palm and then crushed it.
"..." They groaned in disgust.
"Did you know that a person's will could be strong or weak, but at the end of the day it is all subject to the person themselves... and what they experience?~".
"What are you trying to say? Stop using cheap tricks and come forward!".
"How audacious of you to talk about cheap tricks when it is a four against one, hehe~ what I was trying to say is that your will is very strong Nico Robin, worthy of a descendant of that woman".
"..."
The archaeologist frowned, wondering who he was talking about... was it her mother Nico Olvia... or was it where her conjectures were leading her... her mysterious father's ancestry?
"I have eaten the fruit of illusions and nightmares... like this one~" He waved his fingers again and instead of messing around with them, everything changed to a place Robin knew very well. She gasped in silence while Hancock and Primrose wondered what this place was.
As for Gion, she knew very well, that she wanted to tell Robin something but before she could even do it, a woman with white hair appeared in front of the archaeologist, trying to reach her.
"Robin..." She was there, just like the time she left.
"M-Mom..." Robin's hands could never stretch long enough, Nico Olvia's throat was sliced open much to her and the ladies' shock, splattering blood all over in a disgusting fashion.
"MOM!".
For her, it felt like her heart was stricken through.
"That's not your mother, Robin! It is an illusion!" Hancock held her shoulders trying to convince her otherwise, but for her, it wasn't that simple. 
"Hahahaha!! So what if my trick has been given away? You're still feeling pain—just like the wound in your chest... JUST LIKE THE WOUND IN YOUR HEART!"
Primrose crushed a rock with a mere step in utter anger, she showed a protective stance in front of Robin, the one she considered her surrogate child after years of relentless training and teachings.
"I'm Donquixote Cervantes, the Master of Nightmares and 7th Knight, at your service~."
"And I'm Boa Primrose, Robin's surrogate mother... and I'll make sure to kick that disgusting face of yours at least once. Nico Robin! Stand up! I WON'T ALLOW YOU TO FALL JUST FOR THIS NONSENSE!"
"..."
"Didn't you want to stand next to Veyron!? He discarded his past and walked forward... now you do the same! Either embrace your future or be shackled to your past! This is not reality; it is just an illusion. Those that are gone will never come back; remember that!"
Primrose exhaled a deep breath and spread her hands forth.

RUMBLE!!!
A grey aura spread in the world around her, and she smirked when she finally saw a surprised expression on the man's face.
"You, you're a devil fruit user!? Moreover, that fruit..."
BOOOOOOOMMMMMMM!!!!
The illusion itself began to melt like droplets of lava, giving way back to the brightest night of Onigashima, thunder all over, earthquakes and destruction.
"This is my secret trump card... I have always wanted to be hubby's secret weapon. Now that you know about this, I better kill you, Cervantes!"

"That's Leonidas's devil fruit, the Rotting fruit!"
CLAANGGGG!!!!
His spear clashed against Primrose's kick and then, it began to melt down and decompose! The golden color in the weapon receded, taking it back to an appearance of rust and decay, further enraging him.
BOOOOOOMMMMMMMMM!!!!
The kick impacted square against his face, sending him hurling against a rock which considering the amount of strength she had put behind that kick, Primrose was surprised she didn't do any more damage than that, even then... she was satisfied now that she saw his bleeding decomposed nose. 
"You-!"

He flickered away from Primrose's power as more dark arms than he could count protruded from the darkness intending to grasp him.
"Don't underestimate me!"

RUMBLE!!!
Whatever he was going to do, it was going to be catastrophic, the four ladies sensed a gargantuan death aura invade the area, but Primrose wasn't going to allow that, the same grey aura irradiated form her body.

Before the illusion even formed, it had already started to rot!
"You b*tch!"
Primrose smirked and landed, "As long as I know what is it that I'm rotting, I can continue to do it all day, in a way... perhaps my powers are the bane of yours!"

A dome of darkness manifested around the irritated Cervantes who thought they'd attack him jointly, a big mistake.
"Let's go... as long as he's there, Veyron can take care of it!"
Robin, still clutching her chest, created a pathway for them to cross that led to Veyron's vessel; everyone crossed, but then Robin slumped on Primrose.
"Are you?"
Robin delivered a good kiss on Primrose's cheek, surprising the Boa ex-empress.
"Thank you... very much... *sob*," Robin embraced Primrose tightly; perhaps during the last years, this family had been the closest remembrance to a family. Primrose's words just now had literally taken her out of the darkness.
"Anytime, darling~" Primrose kissed her cheek back and carried her like a princess, making Robin blush.
"I'm not a little girl..."
"Sure sure~ let's go... you have worked too much, leave everything to our boy."
"H-Hmn that darkness dome won't last much longer... I used all of my powers to create it, but he's strong."
"Then we better tell him to hurry up!"