Tite Kubo said in an interview recently that he has ideas for the coming 10 years. Now he is on a 3 week break for research XDeasily over 10 years now, and it's only gotten better. They have much more to look forward too. They also still add in new stuff to pick up on. Oda also obviously does his research. Every name, Character, Ability, and characteristic has to intertwine with some figure of either the past, or in his culture. I think that is so amazing.
Something I really love about Oda is that he puts in these little easter eggs everywhere.
Do you remember when Luffy made a prediction about how a merman would look ? (10 years ago)
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Well, Oda did and it appears Luffy was right (Left top):
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