DISCLAIMER: I may forget some of them. This list will be filled progressively as the novel accumulates chapters.
Feelless: Also known as soul power exhaustion. A state in which someone is paralyzed and cannot feel his/her body.
Indigo: A blue fruit with a balance of sugary and salty taste can grow almost anywhere in Iris.
Mana core: A core filled with mana. Used to refill one's mana well.
Soul core: A core containing soul, soul power, and mana that can be found in living beings able to use mana (almost everyone really).
Memory bead: A bead containing the skill and/or knowledge left by someone.
Oath Pact: A contract of sorts engaging two parties' souls until the closes are respected.
Dullahan: Empty armors capable of executing basing fighting moves and orders. Used on the frontline and also for training.
Brum leaves: Leaves of a plant that are smoked to relax the mind.
Fog: A beverage that messes with the mind. Brewed using Brum leaves and additives to create an alcoholic drink.
Inventor: none yet
Boom balls: Basically grenades lol.