Fate/Destiny must exist in some sense...

Let's talk weather a bit. If we could track every single molecule of the atmosphere, we could very accurately predict the future. At least when it came to the future of weather. This is basically meteorology. It's not perfect because they can't track everything though. They have gaps in their data.

Well we also work backwards, so we can guestimate the past also. We can observe things a while, then work backwards beyond the point of observation and figure out where something came from.

So if we could track every fundamental bit of the entire universe we could, using a bit of math, predict the future and understand the past. Including human behaviour. Free will is, ultimately, an illusion because every action, every thought you have had, are having, or will have is governed by the same laws of the universe that created stars and planets and how those things move and how chemistry works, meaning even it can be predicted.