Undertale

A small child falls into the Underground, a place where monsters were long ago banished by humans and now hunt any human they find. You control the child as they try to return to the Surface through hostile environments. Along the way, the game uses a turn-based combat system that blends puzzle-solving and bullet hell elements, alongside other unconventional mechanics.

"Long ago, two races lived peacefully on Earth: HUMANS and MONSTERS. Then, a terrible war broke out between them. After a long battle, the humans won and sealed the monsters underground with a magical spell. In the year 201X, a small child climbs Mt. Ebott. They say those who scale the mountain never return. Seeking shelter from the rain, the child enters a cave and discovers a massive hole. Stepping closer for a better look... the child falls in. And so, our story begins."