Fading Souls || Undertale

Twin sisters Renee and Aria stuck together, always. They were nearly inseparable. One day, the slighter rebellious twin Aria ventured out to Mt. Ebott. Renee followed her, and they both ended up on a journey that would change both their lives.
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After falling to the underground, Aria finds the determination in her soul to reach home again, no matter how many monsters she had to kill. Renee stays by her side, even though she doesn't exactly want to fight the monsters she does what she has to.
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Aria slowly begins losing her sanity as the battles begin to become more merciless. She discovers that she is half monster and half human. Since Renee has the same genetics flowing in her blood, she is the same way.

As the two continue to fight their way out, they also continue to get more blood on their hands. Will they ever reach home again, or will they be stuck in the underground forever, battle after battle as fading souls?