Enter the Gungeon/Touhou style Bullet Patterns?

I'm considering developing a danmaku/manic-shooter bullet hell game for my upcoming college project and was doing some research on how some of the things in the genre works, particularly how to create a flexible bullet pattern system that would allow me to easily create complex enemy attacks like you see in the boss fights of games like Touhou or Enter the Gungeon. Some of these patterns have such intricate detail, they look like they were straight up drawn by hand.

I games like Enter the Gungeon and Furi have a bullet system like this and were both made in Unity, so there must be some sort of way I could achieve this.

Here's a good example of a bullet-pattern system like this: https://www.youtube.com/watch?v=zZu2O_JQ4vs&t

My question is, what's the best way to create my own flexible bullet-pattern system like this in Unity? Should there be a C# script that controls the bullets of each individual attack, or would Unity's animation system be of use? I'm considering something to do with particle systems since apparently having hundreds of particles to act as bullets is way more efficient than if I was using gameobjects, but I the types of patterns I can make would be very limited. Also, there probably needs to be some way to control the attacks through code, for bullets that track the player, etc.