Sanji is a key character. His cooking skills keep the crew fed and his chivalrous nature adds a lot to the story. Another important one is Robin. Her knowledge of the ancient Poneglyphs is vital in uncovering the secrets of the world in One Piece. Usopp also has his significance. His lies and his growth as a brave fighter are interesting parts of the story.
Another couple that fans might consider is Usopp and Kaya. Usopp has always cared about Kaya deeply. They have a long - standing bond from their hometown days. Kaya also has strong feelings for Usopp, and their relationship has elements of friendship and a budding romance.
Luffy will surely be the most important. He is the main character and his journey to find One Piece has been the central plot all along.
Ace himself is the most important character, obviously. His personality, his powers, and his journey are central to the novels. Luffy also plays an important role as his brother. Sabo is another significant character, as they were all like brothers when they were young. And there are the various pirates and Marines that Ace interacted with during his adventures.
Erza Scarlet is crucial. She's a powerful and fearless mage. Her backstory with the Tower of Heaven is really sad and it makes her character more complex. Makarov Dreyar, as the guild master, plays a big role in leading the guild and making decisions. And Happy, Natsu's flying cat sidekick, adds a lot of humor to the story. Without Happy, Natsu's character would seem a bit incomplete.
Eren Yeager is extremely important. He's the main protagonist and his journey from a young boy seeking revenge against the Titans to a key figure in the fight is central to the story. Mikasa Ackerman is also important. She's a highly skilled fighter and has a deep bond with Eren. Levi Ackerman is another crucial character. He's known for his incredible combat skills and leadership within the Survey Corps.
In the Loguetown arc novel, the most prominent character is Luffy. He drives the story forward with his actions and dreams. Then there's Smoker, the Marine who is constantly trying to stop Luffy. Buggy the Clown is another important one. His presence creates some comical and dangerous situations. The Straw Hat crew members are all important too. Zoro's strength, Nami's navigation skills, Usopp's inventions, and Sanji's cooking are all integral to their time in Loguetown. For example, Sanji might be looking for special ingredients while in town.
Luffy is the most interesting. His simple - minded but determined nature to become the Pirate King makes him unique. Also, Zoro is cool with his three - sword style and his loyalty to Luffy. And then there's Sanji, the chef who has his own chivalrous code and is always ready to fight for the ladies.
In my opinion, Brook is an interesting character. He's a skeleton who can play music and has a great sense of humor. Also, Franky, the cyborg, with his super - strength and his unique inventions. And Ace, though his story ended sadly, his relationship with Luffy and his own journey as a pirate were really captivating.
Luffy is definitely one of the most popular. His determination and leadership make him a fan favorite.
Meliodas is one of the most important. He is the captain of the Seven Deadly Sins and has great strength. Elizabeth is also crucial as she has a deep connection with Meliodas. Then there's Ban, with his unique immortality - like power. King, the Fairy King, is important too as he represents pride among the Sins.