Everything rots. Whether it be fruit, or the dirty wall of your grandmother's decaying house.. everything rots. Rotting gives life to scavengers, and scavengers give like to predators quick enough to catch them.

The society you never knew existed underground.. it has rotted. For context, let's start from the beginning..

Long ago, the surface was inhabited by two races: humans and monsters. Until one day, a great war between the two races broke out, ending with the humans being victorious. Monsters were then locked underground by powerful human magic, and left down there for many years. Monsters learned to adapt to living underground, finding that their home could even have a climate of its own with a creation called 'The Core'. The Core was responsible for creating climate, food, and electricity for monsters. During this time, there are two rulers. These rulers are King Asgore and Queen Toriel. One day however, due to complications.. The Core exploded. The explosion killed many scientists, and damaged a great proportion of Hotland. King Asgore rushed for explanation, only able to assume that someone had messed something up. He ordered the royal scientist, Alpyhs, to return to where the explosion had occurred and check for clues.

Alphys did not return for weeks. This worried the King, but he was sure nothing was wrong. They were monsters. They were to be feared, not to fear. But Alphys never returned. Due to the core being destroyed, there was no way to create food or electricity. This left many of the underground in poverty. The King fought to make sure his family was well fed, but Queen Toriel refused to eat.

The King and Queen were overwhelmed with news of a sickness. A sickness that was wiping out too many monsters for either of them to comprehend. This drove Asgore to lock his family in the castle, much to the other citizens' dismay.

You are a special agent, curious about what had occurred. So, you were in the underground searching for answers.