In the sea, The strawhats discover that Nami has caught a deadly fever from Little Garden and since they don’t have a doctor, they’re going to have to take a detour to the nearest island.
They soon see a winter island but before they get there, they are attacked by pirates led by Wapol who has the Baku Baku No Mi which allows him to eat anything and recreate it as a part of his body but since the strawhats didn’t have much time to waste, Luffy flings Wapol into the air and they head back towards the island which they find out is called Drum Kingdom.
Once they arrive on the shore, they are attacked again but this time by the military forces of the king-less Drum kingdom. All of them pointing their weapons at the crew.
Vivi manages to explain their situation and after hearing, the leader of the group Dalton who was a former king’s guard calls of the attack and leads them to the town of Bighorn.
There he explains to them that this island used to be ruled by a cruel king by the name of Wapol who was also the pirate that the strawhats met on their way here.
Dalton explains that Wapol had banished all the doctors on this island except the best twenty whome he called the “isshi-20” and anyone who wanted medical treatment had to beg in front of the king for it.
However one day a pirate named Blackbeard attacked the island and after witnessing Blackbeard’s power, Wapol didn’t even fight back and he instead fled to the sea along with all the rest of his army but Dalton stayed behind.
After being free from Wapol’s reign, the people are slowly making progress in rebuilding their island and now the only thing they fear is Wapol’s return but since Wapol took the isshi-20 with him, the only doctor in the island left is Dr. Kureha who is called a witch by the islanders and she lives in Drum island which is on top of the highest drum mountains along with a type of monster and she only comes down now and then to check from town to town for sick people, taking something from them in return.
After hearing that Luffy decides to climb the mountain with Nami on his back since her condition was worsening by the second and Sanji decides to go along with him.
As they climb the mountain, they get attacked by Lapahns which are giant ferocious rabbits and a fight ensues.
Since Luffy can’t move much with sick Nami on his back so Sanji tries to fend them off but they cause an avalanche and Sanji also gets injured.
So Luffy climbs the mountain carrying both Nami and Sanji.
When Luffy reaches the top, he immediately faints with bloodied hands and frostbite in front of Dr. Kureha and the so rumoured monster Tony Tony Chopper who helps him up.
Meanwhile Wapol had arrived again at the island and he attacked a nearby town to announce his arrival, Dalton tries to fight back but he is brought down, and Wapol starts to head of to his old home Drum castle.
Back at the castle, Dr. Kureha and Chopper are curing Nami while also taking care of Luffy and Sanji.
When Luffy first lays eyes on Chopper who is a reindeer, he starts to chase him along the entire castle along with Sanji to cook him. As carefree as ever now that Nami was in the professional hands of a doctor.
Dr. Kureha then tells Sanji and Nami about Choppers past as Luffy was still chasing him.
When Chopper was just a baby reindeer, he ate the Hito Hito no mi (Human Human fruit) which gave him the ability to walk on two legs and talk. Chopper was thought a monster by everyone until he met Dr. Hiruluk who was a quack doctor who took him in but Hiruluk died after entrusting Chopper who he thought of as a son to Dr. Kureha.
Dr. Kureha had started to teach Chopper all about medicine and now he is even a fully fledged doctor and with the help of medicine he created he can have more transformations from his devil fruit than before.
Eventually, Wapol and his men arrive at the Castle and he is furious to find Kureha and Chopper living in it and it starts a fight.
One of Wapol’s senior henchmen Kurarimo distracts Sanji by throwing sticky hairballs at him which don’t come off. Slowing them down.
This gives time for Wapol to armor up his body with all the things he ate since this is also a property of his devil fruit.
A fight ensues and Wapol aims his canon for the flag on top of the castle which was put on as a memorial for Chopper’s beloved doctor Hirukuk who was the first person to ever accept him.
As Wapol shoots, Luffy hurries to the top and stands in front of the flag succeeding in thwarting the attack which was aimed at the flag.
Wapol decides to change strategies and eats Chess and Kuramarimo and they in return also grow back on his body.
Sanji tries to enter the fight but is stopped by Dr. Kureha since he still hasn’t fully recovered yet so after getting out of his trance Chopper fights him showing his true strength including his genius invention of the rumble ball.
Chopper defeats the Chessmarimo but Wapol escapes only to be found later be Luffy.
After realizing that he is completely unmatched, he begs Luffy for his life, even offering the position of the second in command to the king but Luffy doesn’t care and flings him out to the sky to never be seen again.
In the aftermath, Luffy finally convinced Chopper to join them and as they were leaving Dr. Kureha loaded the canons with a type of chemical that when touched by the snow, the snow would be dyed pink making it bloom like sakura trees.
Therefore the island gets its new name the Sakura Kingdom and the strawhats are joined by their sixth crewmember who takes the place of the ship’s doctor —his dream is also added to the ship going Merry which is to cure every sickness.
As the arc reaches its end, we see a flashback of a man telling the people of drum kingdom to notify Luffy that he will be waiting for him in Alabasta for ten days but the people remember too late as the crew has already left.
The man names himself Ace.