The next campaign I run I want to do a better job of weaving together character arcs with the greater campaign arc. Part of that, I think, is being able to visualize the threads in some way other than walis of text and the idea of some kind of line graph plot came to mind with perhaps call outs to particular events. Or perhaps simply some colored pens to indicate which session focused on which characters?
Perhaps I’m overthinking it? Has anyone done anything like this?
I'm doing this in my current 5e game -- not visualizing, but making the game much more about the PC's interests by weaving that into the narrative. I did this by not really having a concrete plotline to start with -- ie, I had a loose idea to base the start on, but it wasn't something I held tightly to. For me, it was a variant of a multi-piece artifact that does... something to be determined later. The first session was the PC's getting a job to fetch something and stumbling on a piece of the artifact (yeah, I gave an artifact to low level PCs -- and they hate me for it). As soon as that was done, I had their PCs background blurbs (limited to 1 paragraph only) and their BIFTs. From there, I started adding those elements into whatever we did -- usually by throwing multiple triggers at once. Did the party want to help PC1 follow their dream to become the best pit fighter in Sigil, or PC2's desire for wealth and power, or PC3's desire to strike back at the mind flayer's that enslaved him? Putting this alongside the "main" thrust of finding out more about the artifacts meant that the PC's desires were in (mild) conflict with each other and that made them take on more significance.
Now, through play, we've determined that PC1's goal to become a famous pit fighter is secondary to their goal to hunt down their nemesis, a nemesis who is now a primary rival for finding parts of the artifact. PC2 is dedicated to finding the artifact pieces as they see it as the way to obtain the power they desire. PC3 is now working with a mind flayer to fight against other mind flayers, knowing betrayal is inevitable, but is struggling to come to grips with the revelation that they weren't enslaved -- they volunteered. And, PC4 has the ghost of a dead god inhabiting her, whose motivations are as yet unclear but some power beings want to put paid to that ghost and the PC is in the way. Exactly none of this was planned at the start.
As a possibly salient point, this particular campaign has a "no death" rule. PCs cannot die unless the player agrees. If a PC would die, they're taken out of the action, and I get to do something mean. I can overwrite parts of their backstory (this is what happened to PC3), or add a complication (this is what happened to PC4, who hates undeath but is not host to a powerful undead spirit). It also means I can be more free with adding serious pressure to things when warranted. This kind of rule, perversely, has upped the challenge level (again, due to me not having to be nearly as careful) AND put PC arcs more in the forefront as "dying" means that characters find out things about themselves that are challenging and demand to be dealt with. This might not be for you, but I have been pleasantly surprised at it's effectiveness in my game (this is the first campaign I've done anything like this).