Chapter is a term used classify and talk about Eternal's month-to-month Leaderboards, Events, and Leagues. Each Chapter focuses on a theme to explore the game's overall story and to tie together its sets, campaigns, and monthly activities.
Chapters were originally called Seasons. They were renamed starting with Chapter 17: Enemies at the Gates (April 2018), when Eternal became more focused on telling a cohesive story.
Each chapter also includes the release of a promotional card, typically a new Hero unit. In the week after they are released, up to one copy can be earned per day by winning a PvP match. Up to four can be earned in this way over a one-week period, after which they can be crafted.
Every promo is accompanied by a matching avatar. These avatars are released at the same time as the promo card and have thus far never been permanently removed from the store. However, the Milos promo card was temporarily removed due to an unknown bug.