Gear 2 augments Luffy’s blood to increase base speed.
![](http://www.opfanpage.com/wp-content/uploads/2018/10/5426285-4681501-one-piece-luffy-gear-second.jpg)
Gear 3 augments Luffy’s bones to increase mass and attack power.
![](http://www.opfanpage.com/wp-content/uploads/2018/10/Gear_Third_Infobox.png)
Gear 4 augments Luffy’s muscles to increase base speed, attack power (Bound Man), defense (Tank Man) and attack speed (Snake Man)
![](http://www.opfanpage.com/wp-content/uploads/2019/01/unnamed.x97424.jpg)
![](http://www.opfanpage.com/wp-content/uploads/2018/05/maxresdefault-19.x97424.jpg)
![](http://www.opfanpage.com/wp-content/uploads/2019/01/ooo.x97424.png)
My theory is that Luffy, inspired by seeing Kaido in his dragon form, will develop a Gear 5 that will allow him to reshape his skin into scales and harden them with the advanced form of Armament Haki exhibited by Katakuri.
![](http://www.opfanpage.com/wp-content/uploads/2018/10/one_piece_coloring___kaido_dragon_form___op_921_by_dooperco-dcpt1m5-1.png)
![](http://www.opfanpage.com/wp-content/uploads/2018/10/Katakuris_Flame_Haki.png)
These scales will allow his body to stretch while maintaining an impenetrable defense. Adding the blood flow of Gear 2 to the mix could interact with Armament Haki at high speeds like a full body Red Hawk, setting his entire body on fire.
![](http://www.opfanpage.com/wp-content/uploads/2018/10/maxresdefault-19.jpg)
The only thing I wonder with this theory is how he’d maintain the insane boost in speed and strength offered by Gear 4. Perhaps Luffy will learn to develop these normally, as any Non-Devil Fruit user would have to do anyway.
*Theory by cntoruga