I think what you’re describing is similar to an interaction(hit or overlap event) with actors like in-game items or objects.
So, if you’re trying to make a system where interacting with A triggers B, and then interacting with B triggers C (and so on), there are several ways to approach this.
One approach could be using Delegates or Interfaces.
For example, when A is interacted with, you could use a Delegate event or an Interface function to activate B. Then, when B is interacted with, you trigger C in the same way, and so on.
There are other similar methods available, so I recommend checking documentation or searching for different approaches to see what best fits your needs.