Set in the same world as the creators' previous game, Spire: The City Must Fall, Heart's setting is the chaotic undercity beneath Spire. The Heart itself is an artifact — or entity — buried far below the city. The High Elves (Aelfir) who rule the city foolishly tried to tap into the Heart as a power source, accidentally unleashing its power. Now reality beneath the city is weakened and warped, becoming dangerously fluid as you approach the Heart itself.
Some people spend their whole lives beneath the city, living as best they can in the undercity's more stable areas. Others travel from afar to investigate the Heart and its miracles. And some brave — or foolish — souls choose to delve further into the darkness, seeking treasure or glory.
It doesn't usually end well.
Heart: The City Beneath contains the following tropes:
- Angelic Transformation: This is a possible fate for player characters.
- The Zenith ability 'Angelic' allows a Cleaver to become an Angel of the Heart, keeping their own free will for a short time after the transformation.
- The Zenith ability 'Ascension' allows a Heretic to assume the form of an Angel of the Moon Beneath, wreaking havoc in Her name before becoming a bone-crystal statue.
- The Critical Fallout 'Chosen' briefly restores a dying character to life, but then transforms them into an Angel of the Heart.
- Artifact Domination:
- The Cult of Knives is composed of blades that have achieved sentience. They control their "bearers", with each unfortunate body typically impaled by a dozen or so knives, but animated and unable to die despite their injuries.
- Hounds, who draw power from the long-dead 33rd Regiment's badges, can develop a downplayed version when they acquire Zenith abilities. 'Everlasting Stand' allows the original badge-holder's identity to replace the Hound who currently holds the badge. 'Fulcrum' reverses that, with the current Hound's name and identity now absorbed by the badge, replacing the original badge-holder (and perhaps resurfacing one day via 'Everlasting Stand').
- Cargo Cult: The Vermissian network has spawned several of them.
- Played with for Vermissian Knights and Vermissian Sages, who have uncovered some sort of truth and can draw genuine power from their tools and rituals.
- Played straight with Signal Box Cultists, hostile fanatics who modify themselves with fragments of Vermissian materials and technology.
- Forced Transformation: When Hunting the Most Dangerous Game, the Huntress transforms her prey into bestial forms. She leaves their hands intact so that they can still use weapons, though.
- Hunting the Most Dangerous Game: The great Aelfir hunter Lady Salvatious Gryndel came to the Heart seeking the ultimate challenge. For a while, she found it, hunting the monsters of the Heart. Eventually the Heart reshaped her into the being known as the Huntress, and now she hunts people. Although she partially transforms them first.
- Misery Builds Character: Some Minor and Major character beats grant advances when bad things happen, typically when a character takes Fallout harm.
- Order Versus Chaos: The Deep Apiarists are explicitly a force of order, holding back the chaos of the Heart.
- Our Angels Are Different: Angels are powerful, terrifying beings in the service of the Heart. Some of them were once mortals. Or were incubated within mortals. Angels of the Heart are "red and terrible and mighty", and any area they visit reshapes into walls of flesh with eyes opening on every surface.
- Our Hydras Are Different: Carotid Forest is an elderly hydra that realised it could sever its own necks to fuel its growth. Decades later, it has become a moss-covered forest of gently swaying necks — over a hundred of them — with its body buried beneath. It hasn't got much of a mind left, but it's very, very hungry.
- Our Minotaurs Are Different: That-Which-Escapes, the Minotaur, is a huge creature that's theoretically trapped in the true Labyrinth, an other-dimensional prison. Unfortunately, mazes and labyrinths elsewhere weaken the walls of its prison and can become gateways for it. Sometimes, when someone builds a labyrinth below Spire, it starts breaking through to the undercity and the Heart. It would probably be a very bad thing if it succeeded.
- Resurrective Immortality: The Zenith ability 'Perfect Resurrection' allows a Witch to inflict this on their target, at the cost of the Witch's own life. If the immortal is killed, the Heart will recreate them (or, at least, an entirely perfect copy) within a month. There is no known way to stop this.
- Roleplaying Endgame: Zenith beats, and the corresponding Zenith abilities, are designed to end a character arc and retire or remove that character. Each class gets three Zenith abilities - typically, one is activated by death and two are single-use abilities that significantly affect the local area (or the wider world), but will also transform, kill or remove the character.
- Sapient House: The pub known as Last Orders is a sentient, predatory building that preys upon its visitors.
- Scary Stinging Swarm: Deep Apiarists are always accompanied by (and, to some extent, inhabited by) bees. "Release the Swarm" is one of their basic abilities, unlocked at character creation.
- Shout-Out: The cursed and completely inaccessible Vermissian station 'Crescent of the Morning' is a shout out to I'm Sorry I Haven't a Clue's Mornington Crescent game and, via that, to the real-life London underground station of the same name.
- Taken for Granite: This can happen in several ways.
- The Critical Fallout 'Petrified' does exactly what it says. A character touched by the Heart, taking too much stress to Echo, can be permanently petrified.
- The bodies of Heretics who ascend to become Angels of the Moon Beneath petrify into bone-crystal statues after their initial rampage.
