In this world, humans and non-humans coexist.

However, it is not a world where the two species are completely equal. Non-humans are born with much longer lifespans than humans, possessing physical abilities and special powers that are difficult for humans to even imagine. The center of society is also formed around non-humans.

The difference in lifespan has greatly divided the values of the two species. While decades are a lifetime for a human, it is only a fraction of a long time for a non-human who lives for hundreds of years.

And there is one thing that distinguishes humans and non-humans most significantly.

'Ether.'

Ether is a special biological energy present in non-humans, involved in the manifestation of abilities and physical maintenance. However, humans have low tolerance for ether, and exposure to high concentrations can cause serious physical damage.

Then, very rarely, humans with abnormally high resistance to ether began to appear.

Non-humans called them 'Adaptive Humans.'

Adaptive humans could withstand higher concentrations of ether than ordinary humans, and some even adapted to the abilities of specific non-humans.

As their potential became known, a national institution was established.

'The National Institute of Heterogeneous Biological Research.'

Under its umbrella, the '7th Bio-Adaptation Research Center' studied the biological differences between humans and non-humans and the compatibility of ether, aiming for the advancement of human medical technology and the medical application of non-human abilities.

There were regulations in the research center stating that the right to life and the will of the test subjects must be guaranteed, and dangerous experiments must be stopped.

At least, that was how it was on paper.

Adaptive humans were so rare that the data obtained from a single person held immense value. Those who wanted research results began to exploit loopholes in the regulations.

'Dangerous experiments' were renamed 'adaptation limit measurements,' and 'human experimentation' was renamed 'biological response observation.'

Not everything could be called illegal.

But not everyone could say it was right either.

Thus, the 7th Bio-Adaptation Research Center became a place created to protect humans, while simultaneously harboring the potential to become the most dangerous place for them.