Lifespan (Chainsaw Man Supplement)

Life Span System

Lifespan is a biological certainty—an invisible timer written into our cells. For most, it goes unnoticed, until the body begins to wither and fail. Some are born stronger, others frailer, but no two humans are alike. In a world where Devils exist, this fragile number can be manipulated, stolen, extended—or shattered.

This system reflects both the natural variation of human lifespans and the existential horror of beings that can prey upon or play with your time.

Base Human Lifespan

When creating a human character, your existence is timed.

Step 1. Roll a d6 to determine your natural biological aging profile:

d6	Biological Profile	Description
1	Weak Constitution	Your body ages rapidly. Your maximum lifespan is 60 + 2d10 years.
2–3	Standard Human	You fall within typical ranges. Your maximum lifespan is 75 + 2d10 years.
4–5	Hardy Stock	You possess strong genetics and resilience. Your maximum lifespan is 90 + 2d10 years.
6	Outlier	You're a biological anomaly. Your maximum lifespan is 110 + 2d10 years.

Step 2. Roll a d6 again and apply one of the following Lifespan Modifiers based on the result. This represents trauma, hereditary traits, cursed lineage, or unexplained biological quirks:

d6	Modifier	Description
1	-10 years	Born under a bad sign. Your body carries a quiet ticking—cancer risk, chronic disease, or Devil-induced flaw.
2–3	-5 years	Subtle weakness: autoimmune sensitivity, organ underdevelopment, or cursed exposure in the womb.
4–5	+5 years	Your body recovers fast, fights off illness, and shows signs of exceptional stamina and cellular integrity.
6	+10 years	Your bloodline or soul has been touched by something beyond human—science can’t explain your resilience.

Apply this modifier to your Step 1 lifespan result. DMs may override or tweak this based on your character’s backstory or environmental origin.

Devil Influence

Certain Devils—like those embodying fear of aging—may interact with or alter your lifespan directly. This can occur via:

• Contracts that trade lifespan for power.
• Abilities that drain years from your maximum.
• Curses that halt or corrupt your natural growth.

These interactions are permanent unless otherwise stated. A Devil that steals 30 years subtracts it from your max lifespan—not just your current age.

Example: If your max lifespan is 92 years and a Devil steals 25, you will die at 67—regardless of whether you're 20 or 60.

Lifespan as Narrative Weight

Losing lifespan should haunt a character. It's not just a number—it's your future, slipping. A hunter with 20 years left might fight harder... or recklessly, knowing the end is coming.

DMs are encouraged to track lifespan like HP, giving players a growing awareness of their mortality as they tread deeper into a world filled with devils.

Lifespan Contracts

Trading Lifespan for certain benefits is one of the most basic contracts out there, however while detrimental to humans, Devils gain benefits from traded lifespan.

A Devil may store an amount of Lifespan equal to half their Charisma score × their proficiency bonus. If you are the Aging Devil, this is instead equal to your full Charisma score × your proficiency bonus.

While a Devil has Lifespan stored, they may spend it for the following benefits:

Safeguard. As a bonus action or reaction when taking damage from an attack, you may spend up to your Charisma modifier in years from your stored Lifespan. For each year spent, you gain 2 temporary hit points. At 11th level, you instead gain 4 temporary hit points per year spent.

You cannot gain temporary hit points from this feature if doing so would cause your total temporary hit points to exceed one-fourth your maximum hit points.

If you are a Devil with 600 or more Dread Tiers, you may spend up to your Charisma modifier added twice in years.

Refreshed Power. As a bonus action or reaction, when you are below half your maximum amount of Uses, you may spend years from your stored Lifespan to regain expended Uses. You may spend up to your Charisma modifier in years (or twice that if you have 600 or more Dread Tiers, or three times that if stated). For every 5 years spent, you regain 1 Use.

You may only regain a number of Uses up to your proficiency bonus in a single round this way.