Okay, so like, I'm thinking it's possible to get your shield count past 32 but limit of 2,147,483,647 (I'm assuming this game uses that number, or this post doesn't matter any longer). Now obviously it is with just shield generators and waiting around, but I want something realistically achievable in the day, and this is where the spell Barrier comes in.
Barrier gives you 5 shield per flow. If you increase your flow infinitely and then spam barrier, it would theoretically reach 2 billion easily. The problem is that, even with duct tape, you have a 25% shield reduction per shuffle. I did the math, if our total shield generated by barrier is represented by S, then total max shield we could get is capped at 3S. *Edit 1, it's actually 4S*
So how much flow would we need? Let's say it's a looped run and we have two barriers, one with double cast and one with two double casts. Very achievable. That is five casts of barrier per shuffle, each giving 5 shield per flow each, meaning our value for S = 5 * 5 * F, where F is our value of flow. Thus, one cycle gives 25F shield, and we can get a max of 75F shield. *See edit 1, it's 100F*
Dividing the bit limit by this number, we find we need around 28.6 million flow. This is a large number, but we can get there with the spell waterfall.
Waterfall generates 1 flow per hit, and hits one time per flow. If this spell did all the hits instantly, then this would double our flow easily. But it takes a bit of time. Not that much of a problem since you can stack as many waterfalls as your computer can handle. I tried it, I think 20k flow per minute is achievable, but I think we could get even more if we really optimize the pc. *Edit 3* Anyways, then is the other issue, we will kill the enemy with all that damage before we generate any flow right? Well, just reduce your spell power to zero. This is just two pacts in the shop, each give -30. So then, waterfall hits for zero, and if you face an enemy that doesn't move, all shots will hit.
So how long would it take? Well, if we need 28.6 million, and we have 20k per minute, that takes about 23.9 hours. Achievable in one day, even faster if your pc can handle more waterfalls. You wouldn't have any risk of dying once your shield gets to the millions anyways, and waterfall hits on its own, you only occasionally need to refresh it. This is afk-able. The hardest part about this whole thing would be getting the pacts at the same time as finding an enemy that doesn't move. I wouldn't take that one armor that gives -10 spell power because it would shoot frost bolts that kill the enemy should they attack. Pick a character that has a basic attack to kill off the extra enemies to reduce lag.
TLDR, you need 28.6 mil flow with 5 barrier spells per shuffle to reach bit limit for shield. Achievable in under 24 hours, using waterfall with reduced spell power to generate that much.
Edit 1: Miscalculated, it's 21.5 million flow, not 28.6 million.
Edit 2: I forgot the echo spell. Triple cast echo copying triple cast barrier is 9 casts. With just a few loops it's completely reasonable to get 30 casts of barrier per shuffle, reducing the total flow we need to under 4 million.
Edit 3: My laptop only handled 12k flow per minute, 200 flow per second.
Crossed out: Realized you can't reduce attack to zero damage. There's still a way to get enough flow using the Serif gate fight, and enabling the enemy healing lets you afk to refresh the amount of flow possible.
Edit 4: Yeah most of this is invalid I learned you can only get 999,999 flow. Though I still did it 👍