Bleach x OP
So like imagine if Ichigo and his hollow (Shirosaki Hichigo/Ogihci/Zangetsu) are born into the world of One Piece.
They are born as twins to a beautiful mother and silly father who love them so much.
Hichigo was unexpected, since they didn't know they'd have twins, so they give him a bad/unoriginal name, Hichigo.
Ichigo is still Kurosaki Ichigo and Hichigo is Kurosaki Hichigo instead of Shirosaki, but eh.
Hichigo is born with the coloring he has in the original Bleach universe, but even though he is born like that and his eyes look terrifying, their parents still love them.
Ichigo is the twin born 15 minutes earlier than Hichigo.
When their parents discover they are born with powers, they are terrified, but not of them. They are terrified for them.
Their parents try as best they can to protect them, but eventually, they are discovered.
At the age of five, the twins are taken from their home and to science labs.
They are promised to be allowed to see their parents and go back home by the time the scientists are done if they behave and cooperate. They agree, not knowing that the scientists burned down their house with their parents inside.
Did I mention they still have the same powers and abilities as they do in the original Bleach verse? Well, they do. Also Hichigo can lend Ichigo some of his power (*wink wonk* it's similar to being an inner hollow/zanpakuto). The scientists are extremely fascinated in them, especially Hichigo because of his unique coloring and finer control of his powers. They are tortured and abused and experimented on and worn down until they are barely breathing and alive.
In the end, the twins find out the scientists lied to them and killed their parents. They escape and lose control over their powers and obliterate the lab and surrounding towns with them at the age of twelve.
They earn bounties due to that. They're deemed as Kurosaki Ichigo "The Reaper" and Kurosaki Hichigo "The Hollow Demon" although later Kurosaki Hichigo is changed to Shirosaki Hichigo for his pallor. Their bounty is a total of 85,000,000 beri each, higher than Devil Child Nico Robin's early 79,000,000 due to actually being born with their powers and the fact that they're more powerful/feared, especially 'cause they have no limitations like the sea or sea stone. Together, their bounties are a total of 170,000,000 beri. Together, they're deemed The Monster Duo.
Three years later and they're fifteen and hiding on an uninhabited and forested island in the Grand Line. They don't trust anyone but themselves and each other. Hichigo manages to change his coloring to match Ichigo's, but he's still a tad more paler ( he can also change back to his original coloring when he chooses). They stick to similar color schemes with their clothing, Hichigo wearing the opposite of Ichigo. I got this from another fic, but since Ichigo calls Hichigo Shiro, Hichigo calls him Kuro.
One day, they see Luffy, separated from his crew and dropped into the sea by a random large bird, a little after the crew gains Franky as a crew member. When he doesn't come up, they realize he's drowning, and despite not trusting anyone, they still care enough to not let some random dude dropped by a bird drown in the sea. They dive in and pick him up and swim him to shore. Then they do CPR until he's coughing up the water and gasping. After that, they stay to make sure he's actually breathing. When he opens his eyes, they are startled, and shunpo/sonido away.
Somehow, Luffy manages to find them, and asks for food. They give him some of theirs.
Luffy asks them to join his crew. They say no.
He continues bugging them, but it only makes them more paranoid and afraid of him. Eventually, his crew end up arriving at the island, and the twins are shocked because up until now no one's ever found their little island. They hide away as Luffy reunites with his crew.
Meanwhile, Luffy tells his crew all about the kids who are Chopper's age and who saved him and took care of him and how he wants them on his crew.
So the crew go and look for them.
Meanwhile, the twins are on high alert because people are on their island.
So the twins are high up on the trees and move every time they feel someone get close.
Eventually, Luffy manages to catch them and demands they join his crew. They refuse.
Robin recognizes them, because how can she not, when they are like her.
She tells them the story she's heard of them, of how they obliterated and massacred an entire island just for the hell of it at age twelve. How they killed everyone in their way and were extremely dangerous. How the government and the world labelled them as monsters.
The twins hiss and shrink as the crew (except Luffy and Robin) look at them in shock and fear and some give them threatening looks.
Luffy says he doesn't believe it. Robin says she doesn't either.
Luffy's grip on them loosens and the twins dash away. The crew lets them go.
Later, when the crew talks it over, they decide the twins aren't bad. Since they're Chopper's age, it strikes a protective sibling feeling in the older members. Nami mentions that she'd seen fear in the twins' eyes- the twins were scared of them.
So the crew tries to make the twins warm up to them.
They somehow find the twins every time and bring them food or whatever else and just talk with them (Luffy is mostly hugging them) and shares stories of their adventures with them (Usopp lies). Chopper tries to find lots of things to talk about since they're his age.
The twins manage to warm up to them somewhat.
Then people come and they recognize the twins and want to capture them and turn them in for their bounties and the twins are terrified (Hichigo/Shiro is also super pissed, but that's not the point).
The StrawHats won't allow that.
So they fight with the best of their abilities.
The StrawHats get super injured trying to protect them, and the twins can't handle that (they won't let people die because of them again, not like their parents).
So they step in and destroy the enemies.
And the StrawHats are just watching and like woah.
After that, the twins join their crew, but it still takes a while until they fully trust the crew.
After that my idea kind of dwindles down, and there are a lot of holes in this, but eh.