One Piece has been building Kaido's reputation as one of the strongest characters in the entire series for some time now, and the Wano Country arc has given the best look into his power yet. Seeing so many strong individuals working for him is one thing, but it's another to see that he was actually hiding a Devil Fruit power that transforms him into a giant dragon. After exploding onto the scene in the last episode, Kaido has made his big stamp on the Wano Country arc with Episode 913 of the series with a display of incredible strength.
Episode 913 sees Kaido strike the ruins of Oden's Castle by unleashing his Blast Breath, and it was not only an impressive and frightening display of ruthlessness, but this one move also seemingly wiped out the Straw Hats still hiding out there.
The episode saw Kaido come down to the Kuni region of Wano in search of Luffy and Law after finding out that they were hiding out there. He was distracted for a bit thanks to his drunkenness, and decides to fire off at Oden's Castle on a whim. Thinking to himself that it be a good hiding spot for them, but not exactly confirming it for himself, his Blast Breath completely wipes out the castle along with much of the mountain it was sitting on.
But in that moment, the Straw Hats were standing there completely shocked at Kaido's massive form. While they managed to catch that he was firing an attack on them in time, the breath seems to reach them toward the end of the episode as the Straw Hats are completely enveloped in the blast. It's not quite clear if they were able to survive this attack (though fans who have read ahead know the answer), but it's definitely not looking good for the Straw Hats.
Eiichiro Oda's One Piece first began serialization in Shueisha's Weekly Shonen Jump in 1997. It has since been collected into over 80 volumes, and has been a critical and commercial success worldwide with many of the volumes breaking printing records in Japan. The manga has even set a Guinness World Record for the most copies published for the same comic book by a single author, and is the best-selling manga series worldwide with over 430 million copies sold. The series still ranked number one in manga sales in 2018, which surprised fans of major new entries.