Heartbound's story is comprised of 5 acts. A summary of each act is listed below, each including a description of the environment, the color palette and a character list. It should be noted that although Animus, Tower Corp, and Jotunheim are listed as acts 2-4, they may be played through in any order.
Act 1 - Homeworld
Homeworld is the first act of the game. This act takes place in Lore's House, the surrounding forest, The Spine, Trial Between Worlds and ens in the Dark World. The color palette tends to consist of cool, desaturated, and earthy colors.
Act 2 - Animus
Animus is one of three acts available after Homeworld. This act takes place in a village of talking animals, with surrounding areas including a mushroom cave, desert, and pond. The color palette tends to consist of warm, bright, and autumnal colors.
Act 3 - The Tower
The Tower is one of three acts available after Homeworld. It takes place in what seems like a crumbling workplace in a void. The color palette solely consists of red, black, white and rarely gold.
Act 4 - Jotunheim
Jotunheim, being either Muspelheim or Niflheim, is one of the three acts available after Homeworld. The worlds appear to take place in the kingdom of their respective ruler and contain large sections of pipe work. Muspelheim's color palette tends to consist of hot, flame, and earthy colors, while Niflheim's tends to consist of cold, icy, and metallic colors.
For the determination of whether Jotunheim will be Muspelheim or Niflheim, see Paths.
Act 5 - ???
As of writing this, all that is known about act 5 is that it will consist of 9 maps. It should be noted that this is the same number of maps as Homeworld.