Til You Feel It All Around You

Zoro, Usopp and Robin don't return as expected from a foray into an island forest. After setting out to locate them, the rest of the crew finds their comrades each missing significant portions of their whole lives.

A One Piece Fanfic by Tonko, 'Til You Feel it All Around You hits three of the Straw Hats with a Fountain of Youth and shows how their True Companions deal with their sudden Promotion To Parents. The nature of their deaging provides plenty of mystery mixed in with the heartwarming (and at times heartwrenching) tone.

"Usopp: Pirates are coming. Pirates are coming, Mama... Pirates are here."
 * Adult Child: Nami briefly muses on how well Luffy gets along with their newly-younger crewmembers.
 * Bittersweet Ending:
 * Bread, Eggs, Milk, Squick: When shifting through Zoro's locker to find his sword care equipment, Sanji does a mental backspace after realizing he just looked over.
 * Broken Bird: Robin, already.
 * Broken Smile: When Sanji offers the children a false smile to try and reassure them, Usopp actually shows him how to fix it.
 * Brutal Honesty: Zoro, even moreso as a child.
 * Chill of Undeath: According to Chopper, the feel colder than the ambient temperature.
 * Cigarette of Anxiety: Sanji restrains himself from smoking around the kids, stepping out for a couple of these after stressful moments.
 * Constantly Curious: Usopp has plenty of questions for everyone when he's not terrified. Robin's much the same way when emerging from her shell.
 * Creepy Child:
 * Death by Falling Over: Though Brook acknowledges that this may not have been the result if he hadn't reacted quickly to, well, why take the chance?
 * Deconstruction: While it has several sweet, cutesy moments as is par for the course with de-aging fics, the 'older' Straw Hats are painfully aware of how dangerous it is to suddenly have three children traveling the Grand Line with them.
 * Does Not Know His Own Strength: Zoro runs into this problem.
 * Double Take: Zoro gives one of these to Brook, once he stops raging over to actually register that he's there.
 * Empty Eyes:
 * Eureka Moment: Nami and Chopper both have one after Luffy points out that their three regressed friends.
 * False Reassurance: When Zoro demands to know if he's the best yet, Sanji tells him "You haven't lost since the day I met you." He also silently notes that he isn't counting.
 * Fear Leads to Anger: Several times, with Zoro providing a standout example after.
 * After, Sanji silently notes that carrying Usopp back doesn't produce 'warm and fuzzy feelings' like normal; more 'incandescent protective fury'.
 * Fountain of Youth
 * Ghost Amnesia: 'This one' only has the vaguest understanding that they're lost and need to be found.
 * Go Mad From the Isolation
 * Heroic BSOD: Luffy has a brief one upon discovering.
 * Late to the Punchline: Zoro has a varient of this when he finally realizes.
 * Meaningful Echo:

"Sanji: Hell if I know. Maybe Robin does. Did. Would... Will? Damn."
 * OOC Is Serious Business: Nami's disinterested response to Luffy mentioning they might have found treasure along with is specifically pointed out as a sign of how serious the situation is.
 * Oral Fixation Fixation: When trying not to smoke around the kids, Sanji absently bites his thumb. He doesn't even realize he's doing this until Franky points it out to him.
 * Our Souls Are Different
 * Papa Wolf: Sanji swiftly grows into the most prominent example of this, leading Franky to tell him he'll probably make a great father someday.
 * Parental Substitute: Usopp explictedly compares Sanji to his own Mama at times, acknowledging that while she can't be there for him, Sanji's good, too.
 * Protectorate: All of the younger groups automatically become this to their older friends; in particular, Usopp becomes this for Sanji.
 * Shrinking Violet: Robin, but only whenever she decides to join the conversation. She's fine as long as she's not doing anything that might draw attention directly to her.
 * Stepford Smiler: Little Usopp shows signs of being a budding Type A in the vein of Sad Clown.
 * Stripperiffic: Referenced when Nami can't lend any of her clothes to the younger Robin because it's all tailored to emphasize her cleveage.
 * Sympathy for the Devil: Brook immediately empathizes with 'this one' due to his own experiences.
 * Team Dad: Franky continues to act as this for all the Straw Hats, including Papa Wolf Sanji, who directly compares the cyborg to Zeff.
 * Team Mom: Nami, who wonders if there's something wrong with her due to her inability to stop worrying for even a few moments after discovering their crewmates' plight.
 * Tears of Joy: Chopper gets these near the end, upon recognizing that.
 * Time Travel Tense Trouble: Trying to explain things that have/'will' happen to the deaged crewmates falls under this, and Sanji stumbles badly at one point:


 * Toilet Humor: As Usopp discovers very quickly, even the very serious Zoro can't help but laugh at this.
 * Troubling Unchildlike Behavior: All three de-aged True Companions, due to the traumas they're already carrying at their young age.
 * True Companions
 * What the Hell, Hero?: Child or not, Sanji still calls Zoro out after he.
 * Wistful Amnesia: As children, Zoro, Usopp and Robin can't remember anything about their lives past that point, as they haven't lived those events. However, despite not recognizing their friends, they feel safe around them for reasons they can't quite figure out.
 * Usopp, when lying about his adventures as 'Great Captain Usopp', repeatedly refers to actual adventures the Straw Hats have had.
 * You Have Got to Be Kidding Me!: Sanji's reaction when Kid!Zoro starts climbing up the rigging at full speed.