Disclaimer: One Piece still belongs to Oda. However, to the best of my knowledge, all of these characters are original, except for one. If by chance I describe a character that already exists in another fan fiction, please tell me the name of the story so that I may read it. I could always use a good read. Also, there is a minor spoiler concerning Sanji's child, and a major spoiler for Chopper's. A fair warning for anime only fans.
From the Pirate Kings children to the children of his crew mates, with Nami and Robin being excluded, since their children have already been stated in the first bio fic.
Roronoa Muramasa: The oldest of two fraternal twins. He is the son of Roronoa Zoro and Roronoa Tashigi. He has his father's face and green hair, but prefers to keep it as long as his mother's. His training regiment is just as extreme as his father's, which makes sense since he wants to succeed him as the next Three-Swords Style Master and World's Greatest Swordsman. Thanks to the combined efforts of his parents, all three of his swords are of legendary status, just like his father's. However, his first goal is to defeat his best friend, Monkey D. Saul, in a one-on-one fight. Then, he wants to fight and defeat the man he respects almost as much as his father, Adonis. So far, all of Saul's and his battles have ended in either a tie or Saul's victory. He has never even come close to beating Adonis, but he absolutely loves the adrenaline rush he gets whenever he fights the strongest of the Pirate King's children. Muramasa wants to beat Saul at least once before even thinking of challenging his father. He'd be content with at least scratching or disarming Adonis. He has a great relationship with his dad, and greatly loves and respects the man. His is sixteen years of age, making him the same age as Saul. He has tried numerous times to drink with his father. Though Zoro would always indulge in his son's desire to drink with him, Muramasa would always be denied the drink by either his Aunt Nami, his Aunt Robin, or his mother whenever she's on the Thousand Sunny. When Nami does it, she usually punches father and son on the head. When Robin does it, the two usually have to deal with swelling cheeks from countless slaps. When his mother does it, the two have to sit through one of her famous lectures. Yet, despite all that danger, Muramasa still tries to have a drink with his dad. In terms of skill, he's considered one of the strongest swordsmen in the new era, but still not as powerful as his dad in his prime. His skill and prowess with the Three-Sword Style brings pride to his father, especially when he learned how to imbue his swords with Armament Haki. In terms of raw power, he stands as one of the strongest of the Straw Hat Pirates' children. Through the intense training, Muramasa has learned how to summon all of his father's demons, including the Asura. However, Muramasa's personal favorite demon is the Ifrit. He loves igniting his swords in a glorious blaze, burning everything in his path. His destructive power, mastery over fire, and the Ifrit that manifests when he fights gave him the epithet Hell Flame Swordsman. Interesting fact: He has feelings for Kyuju. Only, he's in denial. He's way too embarrassed to admit he has feelings for one of the daughters of the only other man he respects as much as his father. Kyuju is also one of the only girls he has actually gained respect for, especially since he actually lost to her in a few of their sparring matches. The first time he ever lost to her was when he actually started to develop feelings for her, which only grew the more time he spent with her, however rare those moments may be. He knows full well that his feels are not one-sided or unrequited, but he's just too stubborn to admit that he wants to be in a relationship with her. There's also the added handicap that Kyuju is Sanji's niece, and Muramasa argues with him as much as his dad does. Still, it's only a matter of time before he breaks down, and finally admits that he loves the girl. Just takes one good push... and the way things are going, that might not take too long.
Roronoa Kodachi: The younger sister of Muramasa. She may look like her mother, but she keeps her hair short and combed back, loosely resembling her father's hair. Her personality is more on the line of her mother's and has inherited her form of swordsmanship. Her sword is of humble origins, just like her mother's, and she has enough skill to spar with her mother and her cousins. Though she loves her pirate family greatly, she decided to follow in her mother's footsteps, and became a marine. At such a young age, she has already reached the rank of captain, and is one of the most skilled sword fighters the Navy has to offer. She has two dreams. The first one is to help her mother retrieve all of the legendary swords from the hands of despicable criminals, and keep them safe until a worthy wielder comes along. The only exceptions are her brother and father, or those she feels truly deserve the blade they carry. Her second dream is to become strong enough to one day earn the respect and praise of her brother and father. She wants them to see her as an equal, and not as someone they need to protect in dire situations. She hopes to one day fight by there side as an equal so that they wouldn't waste so much unnecessary time trying to protect her. Sonia spars with her the most to help her get stronger. However, the one she rarely spars with is the one she feels helps her grow stronger: Adonis. She believes that if she can at least scratch or disarm him, she would be that much closer to her goal. The fact that that has never even come close to happening helps her further believe that. During one of their few sparring matches, Kodachi was able to unlock Observation Haki, and a weak level of Armament Haki. With the help of her Vice Admiral mother, whom she fortunately directly reports too, she has been able to gradually strengthen her haki. It's only a matter of time before she realizes her dream. Like many highly skilled marines, she has knowledge of the Six Powers. Shave is the one she specializes in, since it's the only one she saw any real use in. Her Observation Haki was far above the level of Paper Art. The wind blades she creates using her sword makes Tempest Kick look like a cool breeze in comparison. She believed a swordsman had no need for a pistol, even a Finger Pistol. Like her father, she believes that scars on the back are a swordsman's shame, but she also believes that an attack on the front is also a sin that can only be redeemed through more training that would prevent any repeat of the incident; making Iron Wall a coward's technique. Moon Walk was a move she already had, thanks in part to her father. Nearly as rare as her training sessions with Adonis, Kodachi gets to train with her father. Unlike her brother, she didn't master any of her father's demon auras, but developed on for herself. Zoro was extremely proud of his daughter when she made her own demon. It was the Garuda. When Kodachi first materialized it, it took the appearance of a beautiful, green-tinted woman with powerful wings; practically a green angel. When materialized, Kodachi gets an arsenal of wind-based attacks. Her wind slashes rival that of her father's Phoenix techniques. She even has her own tornado attack that Zoro himself would one day outclass his own. The demon even allows Kodachi to fly. When she first used that skill on a mission, many of her subordinates thought it was Moon Walk. However, when actually users of Moon Walk saw her use that technique, they realized that her technique was at a much higher level than Moon Walk could ever achieve. Some believe that she is almost as fast as Kizaru himself. They are partially correct. Kodachi still doesn't have full mastery over her Garuda, but when she as full control, she should be just as fast as Kizaru. Her skills with the sword, her wind techniques, and her natural beauty gave her the epithet of the Wind Blade Maiden.
Riku Violin: The daughter of Sanji and Riku Viola. She inherited all of her mother's looks, something Sanji is happy about. He'd rather his daughter look like her beautiful mother than even remotely resemble the Vinsmokes. She has no knowledge of her Vinsmoke heritage, and doesn't even know Kyuju is her cousin. Though Kyuju does know this, she'd rather keep it a secret from her cousin. Violin is a skilled dancer like her mother, and was even taught her fighting style to keep herself safe. She was also taught a thing or two about cooking for her father, which she used to bake one of her mother's birthday cakes. The entire family, including herself and her father, greatly enjoyed the cake. Some of her favorite past times are dancing with her mother, enjoying her father's delicious food, or enjoying the company of Kyuju and Scarlet. She adores her Aunt Rebecca and Granduncle Kyros. She knows about her granduncle's past, but still loves him. Her grandfather is also precious to her, and she tries her best to help out her mother and grandfather in any way she can. Her favorite stories are her granduncle's past as the strongest gladiator, and the story of how her Uncle Luffy, or "Lucy", defeated Doflamingo. As the crowned princess of Dressrosa, she studies daily so that she can grow up to become a great ruler that will keep her home country safe and happy.
Haysopp: The son of Usopp and Kaya. He inherited his mother's blonde hair, but it's as curly as his father's. He is also fair skinned like his mom, but has his dad's nose. He inherited his dad's bad habit of telling lies, but also inherited his sniping skills. Like his dad, he prefers to use a sling shot instead of a conventional firearm. When he was of age, Usopp gave his son his old Kabuto slingshot, a gift that made Haysopp cry tears of joy. Of course, it caused his dad to cry tears of pride, and his mother to cry tears of happiness. Eventually, through much training with his family, he unlocked Observation Haki. He is one of the few people who can say he beat Adonis at anything. His skills with the Kabuto outmatch even Adonis's Dark Pistol, the proof being Haysopp's many victories in their sniping battles. The only people Haysopp can't beat are his dad and grandpa. Another thing Haysopp inherited from his father is his brilliance, and has created many amazing tools and weapons that he used to further upgrade his new Kabuto. He has also crafted items for his cousins as well, who all found awesome uses for the inventions. His sharpshooting skills and the knowledge of him being the son of Usopp, who has been revealed to be the original Sniper King, gave him the epithet of Sniper Prince Haysopp. Later, he was eventually called Demigod Haysopp after (accidently) liberating a slave colony.
Joey: The adopted son of Franky. His design is based off of Mechanic by Xeromander on Deviant Art. A handsome young man with a well built body, he usually hides his face behind a mask. It is actually quite rare for anyone to see him without it, even his dad. Unlike his adopted father, he isn't a pervert or a cyborg, though he thinks have a cyborg for a dad is ridiculously badass. He sometimes even brags about it, which makes Franky cry, seeing how much his adopted son loves him. He is just as skilled a shipwright as his dad, and every bit as tough and chivalrous. He will never back down from an honorable fight between men, nor will he ever question the lifestyle of a true man, no matter how strange. In terms of fighting, he'll either use his fists or his favorite wrench. In absolutely desperate situations, he'll use his custom built chainsaw, which was tested to be strong enough to cut through seastone as easily as a hot knife through butter. He also found out that it was strong enough to cut through a Haki infused blade, thanks to Kodachi sparring with him with a common marine sword. He won't tell anyone how he made it, not even his father. He also builds other weapons and tools, and even built his own giant robot. Franky was so proud. Even the cool and collected Saul couldn't help but marvel at the invention. His dream is to one day create a ship that can not only sail through the seas, but through the very stars themselves. His genius intellect and inventions gave him the epithet Mechanic Joey.
Tina Tina Chopper: The daughter of Tony Tony Chopper and Milky, the Reindeer Mink that stole our favorite doctor's heart (chapter 814, pg 14; her name and image was shown in the last panel of chapter 807... on the back of the mink at the far right... Am I the only one who thinks that's a cheeky Easter Egg, or just plain cheating?). She usually goes by Tina. An absolutely adorable Reindeer Mink. She as the same weakness as her father: You call her cute, and she'll try to deny it while doing a happy dance. She thinks here father is ridiculously cool, especially his ability to transform into different forms. Her favorite of his forms is Kung-Fu Point, since she can actually imitate that form. She was not only taught her father's Kung-Fu fighting style, but also his medical knowledge. She has even worked as her father's assistant from time to time, and was told by Chopper himself that she would be a great doctor one day. That was one of the greatest moments of her life. It actually happened on her hardest assistance yet: Trying to heal a heavily wounded Adonis. Though he was covered in cuts, bullet wounds, and sickly purple bruises; all the while losing blood, she was able to keep her cool and help her father heal another precious member of her family. She turned a deep shade of red when Adonis thanked her and praised her skill as a doctor. She didn't do her happy dance at all. She just stood there and happily accepted the praise, promising herself to become an even greater doctor. One marine saw her eating candy happily, so they government gave her the unfortunate epithet of Candy Loving Tina with a measly 50 berry bounty. She was just as dejected as her father when he got his name and bounty, for both the name and painfully low bounty.
A/N: And that's the end. I couldn't think of a child for Brook... for obvious reasons. If one of you somehow can, send me a PM, and I'll add it to this, giving you the credit of course. Like with Children of the Pirate King, if you want to borrow the kids for a story, send me a PM so I can keep a look out for a good story. I'm always looking for a good read.