So I'm a big fan of the worldbuilding in one piece, but at times Oda does just toss things in there without major thought, and they are often thrown into array by later events. Many character powers pop up through the series and never get expanded on, but I think outside of devil fruits and haki there is actually a decent source of all this crazy stuff in the world.

The basis of all of this is Semei Kikan(Life Return) and to a lesser extent the Rokushiki. Now while most members of CP9 are pretty irrelevant by now, the wide extent of abilities and applications of their skills they showed through these techniques is quite impressive. Some like Soru and Rankyaku have been achieved with pure stats or weapons, so I don't think they are super important.

I chose Sanji as the topic of this study as he has abilities that are in vein of these concepts, and we learned that germa enhancements don't always need to be on.

Tekkai and Iron Like Skin

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https://preview.redd.it/sanqpbljscsc1.png?width=284&format=png&auto=webp&s=c66038193968c1176caf3f67d614ae46099d03f4

We see that Sanji and his siblings all have this metal like body that seems to harden around sharp attacks and shape itself around blunt ones. Through panels like these we know that while tough, it is also malleable. I believe this ability stems from both Tekkai and Kami-e, with a little bit of life return.

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https://preview.redd.it/h9ltlfwhscsc1.png?width=1000&format=png&auto=webp&s=8357d1bb32800b83a97fe215d03e537ec72e66e4

Zipper mouth here can make his body like slime through Kami-E, and we see that Lucci can even alter his zoan form using these techniques in tandem. I suspect that since Sanji barely feels pain while in Germa form, that him getting his limbs broken and stuff is actually just them being bent out of shape, and then life return puts them back in place, something that his siblings cannot do. Seeing as he learned Geppo on his own, I don't think these powers are as exclusive to the government as we thought.

I believe that these three techniques can explain any mainly physical strange powers in one piece along with people like Lao G and his old man powers. If anyone has questions about any Body based abilities I would love to hear your questions or characters who may disprove his while I start thinking about how people harness elemental powers like fire. I am starting to think that Sanji may just be using life return to heat up his body.