Tropes A to B (Adaptation-Induced Plot Hole, Arc Villain, Berserk Button, Beware the Silly Ones, Big Brother Instinct, Bowdlerise, Break the Cutie) | Tropes C to D (Call-Back, Chekhov's Gun, Cliffhanger, Combat Pragmatist, Crouching Moron, Hidden Badass, Curb-Stomp Battle, Dark and Troubled Past, Deconstructed Character Archetype) | Tropes E to F (Early Installment Weirdness, Famous Last Words, Foreshadowing) | Tropes G to J (Heart is an Awesome Power, Hypocrite) | Tropes K to M (Laser-Guided Karma, Logical Weakness, Mass "Oh, Crap!", Moral Myopia, Muscles Are Meaningless) | Tropes N to P (Nice Job Fixing It, Villain, Oh, Crap!, O.O.C. Is Serious Business) | Tropes Q to S (The Reveal, Shout-Out, Spanner in the Works, Superpower Lottery) | Tropes T to Z (Wham Episode, Wham Line)
- Fukaboshi, Ryuboshi, and Manboshi towards their younger sister Shirahoshi. Fukaboshi in particular puts his life on the line when protecting her from Hody.
- Portgas D. Ace is very protective of his adoptive little brother Luffy. This goes from taking on Blackbeard to sacrificing his life against Akainu. The brotherly bond between himself, Luffy, and Ace is what Sabo valued the most. In the present storyline, after revealing himself to be alive to his younger brother, Sabo makes it clear to his enemies that he would do anything to protect Luffy, especially after losing Ace.
- Tony Tony Chopper's relationship with the older males of the crew screams this trope:
- Zoro to Chopper, who keeps an eye out for the little guy and becomes upset when anyone hurts Chopper. Zoro also gives Chopper advice on being a man during the Davy Back Fight when Chopper was forced off the crew and was blubbering like a baby. In one of the cover requests, Zoro’s dream shows he appreciates Chopper’s admiration of him.
- Sanji to Chopper, despite being rough with the rest of the males on the crew, Sanji treats Chopper with genuine affection, like patting his head when he’s scared and even giving him shoulder rides. Sanji also gives Chopper guidance like Zoro does.
- Luffy and Usopp aren't quite as big brotherly to Chopper as Zoro and Sanji are, but they still goof off like siblings and Luffy is the first person to call Chopper his "friend", which brought the reindeer to tears. Usopp tries to play cool big brother to Chopper by lying about his great accomplishments, which Chopper is too naive to see through it.
- Chopper himself finally gets to play big brother to Rabbit Mink Carrot in Whole Cake Island, and asks her to call him "Brother Chopper" but Carrot just says "Cho-bro".
- Sanji is also like this towards Carrot, protecting her from Daifuku’s Genie and giving her a Cooldown Hug when she was upset about Pedro.
- When Trafalgar Law was offered a (false) way out of Flevance as a child, he refused to leave with the other children because his little sister Lami was still sick in the hospital.
- Zoro to Johnny and Yosaku, inciting them to call him "big bro Zoro", which he dislikes.
- Cool Big Sis version with adoptive sister Nojiko to Nami; her sisterly care includes getting a tattoo of her own after Nami was forced to get one as well by Arlong to show solidarity with Nami and make her feel better, and taking a bullet for her sister when the Marines arrive.
- Robin, likewise, also takes a "big sister" role for Nami soon after joining the crew.
- Nami, likely inspired by Nojiko, plays big sister to Vivi, Aisa, Momonosuke (despite his pervertedness), the Punk Hazard kids, Carrot, and Tama, even directly referring to herself to Tama as "Big Sister Nami".
- Luffy, Zoro, and Usopp's relationship towards Nami can be easily seen as brotherly (Sanji being the exception), especially as seen in Arlong Park where they annihilate the Arlong, his crew, and fortress after seeing Nami cry. Zoro and Usopp often bicker with Nami but will do everything in their power to protect her if she's in danger.
- Franky as the father/big brother figure to both the Franky Family and the Straw Hats gets a lot of this, he refers to Mozu and Kiwi as his "little sisters" and treats Nami in similar fashion. Franky went on a Unstoppable Rage when Luffy and the others attacked the Franky Family, plus Usopp and Chopper were reduced to blubbering tears when Franky saved them from zombies in Thriller Bark (even calling him "big bro"). In Wano Nami has a similar moment when Franky saves her from Big Mom, giving him a big hug which Franky reacts to with a paternal smile.
- He's even like this towards his adoptive older brother, Iceburg. Although they act estranged and constantly bicker with each other, Franky was both devastated and absolutely furious when he learned that CP9 had (falsely) assassinated his brother. He shows genuine concern about Iceburg's extensive injuries later, too.
- Marco towards Ace and later Luffy. When Ace asked why the Whitebeard pirates would sacrifice themselves for him, Marco — normally The Stoic — boldly roars back that nobody messed with one of their own. And after Ace died, he led the rest of the Whitebeard Commanders to protect Luffy.
- Despite his sadistic nature (thanks to his birth), Niji did express concern when his older sister Reiju was damaged by Big Mom, but eldest son Ichiji waved it off saying it was her fault for "being weak". Sanji puts them both to shame, directly saving Reiju from being killed by Big Mom. Ichiji, Niji, and Yonji did protect Sanji on Cacao Island, but didn't do it out of brotherly affection. Only Reiju claimed she'd kill anyone who hurts her little brother.
- Charlotte Katakuri is this to all siblings, including his older brother Perospero. Luffy gets brutally curb stomped when he tries to attack the Charlotte children in front of Katakuri, and him trying to beat Katakuri's favorite younger sister Brulee doesn't help.
- Dark Action Girl Ulti of Kaido's Flying Six is this to her little brother Page One; she may get violent with him herself when she's annoyed and (somewhat unintentionally) treat him as a punching bag, but anyone else doing so is a surefire way to piss her off.
- Momonosuke trains hard in Wano because he wants to protect his younger sister Hiyori from Shogun Orochi. Ironically, thanks to Time Travel, Hiyori is physically 20 years older than Momo and already a Cool Big Sis to her kamuro Toko.
- Also in Wano, Ace was this for Tama, and Luffy effortlessly takes his place and goes particularly apeshit whenever she gets hurt. Later on, Zoro, Sanji, and to a lesser extent Usopp invoke this towards Toko, and Robin is protective of her as well. Nami also gets furious when Ulti hurts Tama during the Final Battle.
- Back during their days as crewmates of the Xebec Pirates, Big Mom herself was something akin to a sisterly mentor to Kaido (who was a teenager at the time). As such, while their current relationship is that of rivals due to their statuses as Emperors upon sensing that Linlin was defeated Kaido can't help but howl in anguish as he reminisces about how they once promised to seek the One Piece together.
