Season 3

After Jack and Frisk became the rulers of the underground, they gave born to their daughter Charlotte, who has a pure Confidence soul. Gaster discovered that people with such soul were extremely dangerous; they could barely control their feelings, and they had severe behavioral problems. Gaster warned Jack that there was a high chance that Charlotte will ruin the whole underground and cause harm to his people, especially when she was on such a high political status.

Gaster stated that it was best to end her life with mercy. Jack followed his advice and decided to kill Charlotte. However, Frisk discovered his plan and she was not happy with it. She didn't know what Charlotte will do to the whole empire. With great disappointment, she divorced Jack and left the throne with Charlotte, who was still a baby and had totally no idea of her father's plan.

After that, Frisk and Charlotte lived in the Ruins. Frisk raised her daughter with great care, and soon Charlotte becomes a teen. But what Gaster said was right; she always cried for no reason during nighttime, and she caused many trouble to her friends and peers.

Monster Kid is a Royal Guard of Jack's. He was treated badly by the other guards in the castle and he wanted to be promoted to a higher position so that no one dares to show disrespect. He tried to defend the kingdom with all his might, but no one got to know his hard work; not even the king. One day, he noticed that Jack was totally depressed and lonely after Frisk left him. With that, he created a human-looking bot Susan, who was programmed to love the king and replace Frisk's former position.

When Jack discovered Susan, he wrecked her immediately and sent her metal body to the incinerator. "No one can replace your position, Frisk. You are forever mine and I will be the one waiting for you."

Knowing that his creation is destroyed, Monster Kid exploded in anger and was determined to overthrow the king and redeem the throne himself. He got to know Jack's plans for killing Charlotte, so he ran off to tell her everything and told her to be careful. He even tried to add hate to Charlotte's locket to make her a tool purely for revolution.

Monster Kid knew that he succeed when Charlotte became extremely disappointed and angry with her father. He guided her way to kill the king by filling her vessel with hate.

Soon, Frisk got to know Charlotte's plan for killing her ex-fiancé. She realized that she had been totally wrong about her daughter, and she decided to go back to the castle to protect Jack. That night, Frisk apologized to Jack, and they got reunited again.

A few days later, Charlotte and Monster Kid started invading the castle. They wounded and killed many royal guards and Jack was almost dead. Seeing this, Frisk came up to stop her daughter. In anger, Charlotte stabbed Frisk to unconsciousness. Jack had no choice but to kill her for the sake of monsters and humans. "Charlotte, my dear daughter...no, whoever you are, why do you have to bring us so much heartache? Now, it's time for you to pay. It's time for you to go. Goodbye." After a great number of treatments, Frisk was alive and well. The pair of lovebirds rejoiced, and they are confident and determined to rule the underground, and bring their people hopes and dreams.