Sparks are Everglow's credit. Every chapter costs a fixed number of sparks, you start with 100 and top up when you choose; no subscription is required. The name is literal: each spark lights one chapter.
A credit balance instead of a mandatory subscription exists for a simple reason. You don't read the same amount every month. Some weeks belong to one story, some to none at all. Sparks wait until you come back, and the billing stays neutral with no hint of what you've been reading.
Sparks pay for every chapter of a catalogue story and for the chapters of a world you build yourself, which you can set up from 20 sparks. What you read stays private: no profiles, no likes, no shared links.
The first 100 sparks are yours at the start. That's enough to read far enough into a story to know whether it has hold of you. Whether and how you top up afterwards is your decision, and the chapter prices don't change.
At Everglow you do not just read it. You are the protagonist, and every chapter ends with your move.