The Uo Uo no Mi, Model: Seiryuu is one of the strongest Devil Fruits in the world of One Piece. It is a Mythical Zoan power that allows the user to transform into a giant eastern dragon and its hybrid and it will. Eaten by one of the former Four Emperors of the Sea, Kaido, this Devil Fruit is exceptionally overpowered and fans have seen its devastating powers in the Wano Country arc extensively.
One of the biggest assets of this fruit is that it provides the user with an impenetrable armor that can only be damaged or bypassed using a select few abilities. As such, in the world of One Piece, there are only a few counters to this powerful ability.
6 Seaprism Stone
Being a Devil Fruit, it is no surprise that the Sea Prism Stone is one of the counters to it. Since this stone emits the same wavelength as the ocean itself, it becomes a big weakness to every Devil Fruit user. As such, it is a standard weakness of the Uo Uo no Mi, Model: Seiryuu as well.
As far as fans know, Kaido has not been put in Sea Prism cuffs in the series to date. However, there is no reason to believe that it wouldn't work on him. Damaging Kaido should very well become possible using Sea Prism Stone.
5 Fishman Karate
Fishman Karate is one of the very refined arts in the world of One Piece that allows the user to manipulate the moisture in their environments. Since most bodies are largely composed of water, Fishman Karate becomes a way to channel power inside their bodies and do damage even without hitting them. Essentially, a user of fishman karate can bypass Kaido's scales without even having to touch him.
Of course, this doesn't mean that every user of Fishman Karate can deal damage to Kaido. However, what it does mean is that if a user of Fishman Karate who is extremely strong does fight him, they will most certainly be able to bypass his Devil Fruit durability.
4 Hasshoken
Hasshoken is another martial arts style in the world of One Piece that relies on the usage of shockwaves. This fighting style is predominantly used by the people of the Kano Kingdom. Using Hasshoken, they can channel vibrations within any body and destroy them from within.
Even the toughest of defenses can be damaged with Hasshoken and, similar to Fishman Karate, it can bypass Kaido's defenses. Of course, for anyone to do significant damage to Kaido using Hasshoken, they would have to be a very skilled user of this art and strong enough to compete with the likes of the Yonko in the first place.
3 Certain Devil Fruit Powers
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Certain Devil Fruit powers in the One Piece world are great enough to bypass Kaido's defenses. For instance, the Ope Ope no Mi allows the user to deal damage from the inside, bypassing their defenses with ease. Law used this ability on Big Mom and was able to damage her severely from the inside.
Similarly, there are other Devil Fruit abilities that would allow the user to bypass Kaido's tough defenses. Blackbeard's Yami Yami no Mi would simply nullify Kaido's Devil Fruit powers and allow him to damage the monster. There are other Devil Fruits in One Piece that can have a similar effect on Kaido and these fruits would certainly work as perfect counters to this ability.
2 Internal Destruction Ryuo
As always, Haki is an effective way to counter any Devil Fruit power, and Kaido's Uo Uo no Mi, Model Seiryuu is no exception. Using Internal Destruction Haki, a user can make their Haki flow directly into the body of their target and deal damage from the inside. The Akazaya Nine used this power to damage Kaido and, later on, Luffy also demonstrated this ability in the fight against the Yonko and injured him.
However, on its own, this Haki is not effective enough to cause any serious injury to the Yonko. According to Luffy, the damage that he was able to throw Kaido's way using Internal Destruction Haki was simply too shallow.
1 Conqueror's Haki
Conqueror's Haki is, by far, the most effective way of countering the incredible durability offered by the Uo Uo no Mi, Model: Seiryuu. Zoro was the first person in the arc to use Conqueror's Haki to damage Kaido, however, his wound didn't appear to be serious enough, even though it left a scar. Luffy managed to grasp this concept shortly afterwards and was able to put Kaido on his back immediately.
By increasing his hold over this power, Luffy was able to level the playfield with Kaido and consistently hurt him throughout the battle. After Awakening his Devil Fruit powers and combining them with his newly awakened advanced Conqueror's Haki, Luffy managed to defeat Kaido and become one of the strongest pirates in the One Piece world.