How do you plan for a story with multiple overlapping arcs? In One Piece, you have one big story arc, and then multiple arcs within it (2 layers), but I am wondering if it's possible to have a story with multiple overlapping arcs (10+ layers or more), and if it is possible, how do you plan for it, because when you write a beat sheet, you only write the main story arc, so in the case of multiple overlapping arcs, your story may end up with a lot of plot holes, pacing and logic issues, so I was wondering if there was a way you can plan for a really complex story like that.
When writing complex arcs, it's best to start with one overarching plotline. The one that draws all the characters in. You need to have a clear beginning and the ending in place, so that everything fits tidily in there.
Then think up a subplot that does not take away the power of the first plotline, another mystery to tease the reader. After that, think of the emotional journeys of the key characters. What do they need for a fulfilling satisfying ending? Get their endings down. These characters should be fully fleshed out, with believable motives. Add in a few red herrings. And now you have a bunch of plotlines.
To organize them: I use the headings feature on Word and Google Docs. For KEY plotpoints, I write in the largest headings, along with a small paragraph of everything I want to have happen. For secondary, I use smaller headings, and for emotional or other side plotlines, I use the comments to keep them all in line.
Basically, you need to plan thoroughly, being a pantser will lead to plotholes that need significant editing to bring up to snuff. Good luck!