The series' starting point — what the first episode establishes and how it works as an opening.
The opening episode of a long series matters less for plot than for teaching the audience the rules the work runs on. One Piece's first episode nails down what the protagonist wants, how unreasonable that goal is, and why he means it anyway. The attitude that will repeat for hundreds of episodes — move forward toward the goal — gets its reference point here.
It does not explain the scale of the world at once. It starts on a small stage and merely implies that something far larger lies beyond. That is the classic long-form opening design: keep the information the viewer must absorb right now to a minimum, while making the eventual scale something to anticipate.
The first chapter and the first episode cover different ground at different speeds. Animation has airtime to fill, so scenes are added or extended, and music and voice performance change how the same moment lands. Manga instead controls pace through the space between panels and reads much faster. Neither is better — the two media are using different tools.
Early episodes can feel unfamiliar, since art style and directing conventions have shifted since. But the motivation established in episode one keeps operating throughout, so watching it once rather than skipping ahead makes the emotional through-line of later arcs easier to follow.
Each button runs this keyword on that search engine