Crunchyroll and Funimation, which are the legal sources of One Piece, has some sort of a free trial.
Where can I watch all anime legally?
- Anime list on Netflix https://www.netflix.com/
- Anime selection on Hulu https://www.hulu.com/
- Anime lineup on Amazon Prime Video https://amzn.to/3aSStMS.
- Anime list on YouTube Movies https://www.youtube.com/
- Top page of Crunchyroll https://www.crunchyroll.com/