A common theme is the power of friendship. Despite their differences, Chara and Sans can form a bond that helps them both grow. Another theme is the exploration of good and evil. Chara has a complex moral standing, and Sans is often seen as a more morally 'good' character. Their relationship can be used to question what is truly good or evil.
One of the themes is the concept of second chances. Chara may have made mistakes in the past, and through their interactions with Sans, they are given an opportunity to start anew. Also, the theme of understanding the other side is present. As they come from different backgrounds and mindsets, they learn to understand and accept each other, which is a key part of many such fanfictions.
Many undertale chara x sans fanfictions explore the theme of trust. Given Chara's history and Sans' own cautious nature, building trust between them can be a central plot point. Additionally, the theme of sacrifice might be present. They might be put in situations where one has to sacrifice something for the other, which deepens their relationship and shows the depth of their connection within the fanfiction.
Chapter 332, ", Titan is completely done", is the clearest early answer because it turns Alliance's situation into a concrete plot event. The chapter turns that into something concrete by moving from Eleven Knight Titans, more than nine hundred Sentry Mechas, five... to He was no stranger to hardship, nor was he a pampered prince..
Chapter 347, ", I am the Korolya Governor.", is the clearest early answer because it turns Gu Hang's situation into a concrete plot event. The chapter gives readers a real answer by opening on You're too impulsive," After the meeting, Wang Qi was criticizing Gu... and ending on No matter how the battle turns out in the end, for now, the Gu.... In story terms, the chapter closes with Gu Hang and Lois were at best acquaintances, hardly even friends, let alone insiders.
Chapter 380, ", It is necessary to maintain respect for Gu Hang", is the clearest early answer because it turns Gu Hang's situation into a concrete plot event. The setup is Regarding how much tax each world should pay, the Empire had..., but the pressure keeps building through For planets like Rage Owl Star, Heijian Star, and Korolya, which all....
Chapter 423, ", My Hero", is the clearest early answer because it turns Flying Wing Star's situation into a concrete plot event. The chapter turns that into something concrete by moving from Yelisia felt somewhat nervous, for she didn't know exactly what Gu... to One rocked back and forth on a reclining chair, the other sat beside,.... What makes it stick is that the chapter closes with The Dragonhawk and Rage Bear Star Realm Army Corps would remain on Steel Wing Star as defense forces.
Chapter 329, ", Heijian Star Joins the Alliance", is the clearest early answer because a shaky connection becomes usable in the plot. A useful checkpoint is the way the scene starts with In a sense, the Fatches Family could be considered to have 'brought... and follows through with Thus, the last political obstacle Gu Hang faced on Heijian Star had....
Chapter 393, ", Hongjian Star Joins", is the clearest early answer because it turns Rage Owl Star's situation into a concrete plot event. The chapter turns that into something concrete by moving from Regarding the reforms of Fatchess Tri-Star, even if the plan devised... to This is still achieved under circumstances where Korolya has suffered....
Chapter 358, ", Iron Heart", is the clearest early answer because it turns Ge Wajia's situation into a concrete plot event. Early on, Gu Hang's actions at this moment were all for the purpose of creating.... By the end, This was not easy, and on top of that, there was something constantly.... Inside the broader family politics storyline, the chapter closes with The third scene was his farewell to his family., which gives Ge Wajia a stronger narrative position and pushes the power growth onward.
Chapter 304, ", The Way to Return to Rage Owl Star", is the clearest early answer because it pushes Zhang Guang into a new phase or setting. A useful checkpoint is the way the scene starts with There's nothing we can do then, everyone has to wait here. and follows through with The commander of this force was the Colonel of the 3rd Beast-slaying....
Chapter 420, "Terrifying Spiritual Energy, Tearing Through the Ship's Shield (Part 3)", is the clearest early answer because it turns Storm God Kingdom's situation into a concrete plot event. It opens with On the bridge of the Concerto, Gu Hang stood with his hands behind... and closes on Without shields and with a flawed structure, the orc flagship....
Chapter 400, ", Korolya Pays Taxes", is the clearest early answer because it turns Shang Yanwen's situation into a concrete plot event. The chapter gives readers a real answer by opening on Late into the night, the conversation had already ended when Shang... and ending on Comrade Shang, you've come at just the right time!.