Another constant theme is that of friendship and the ties that unite human beings, mainly those between Luffy and his ragtag crew. After all, even the most powerful captain needs others to manage the ship: he won’t survive without a group of people supporting him through good and bad weather. Of course, even the most harmonious of friendships have their weak points, and the crew members many times end fighting and bickering among themselves, even to the point of abandoning the ship, though never for long.

           Finally, we get the matter of prejudices, both social and racial. At the early stages of the manga we meet Arlong, a fish man and his crew, who have enslaved the entire human population of an island, charging them heavy taxes under the menace of slaughter. In other islands, however, the situation is the opposite: there, the fish men have no rights, and they can be murdered or enslaved without penalty. In these situations, Luffy’s crew always takes a stand, which generally means a huge amount of property damage and laying the smack down on the offending party.

  Wrapping all up, One Piece is a very long saga: it started in 1997 and has continued without significant interruptions until today, with more than 650 episodes in the manga and 500 in the anime. It shows a surprisingly original take on the classic themes of the coming of age and journey of the hero. Its strongest points are the solid character development and the way it shows the thriving world in which they live. Its creator, Eiichiro Oda, is an excellent narrator, and the series always leaves one eager to keep reading, in order to know what new adventures are in store for Monkey D. Luffy and his crew.
From: http://fantasy-faction.com/2013/one-piece-manga-series-review

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