A frequent theme is the contrast between the earthly and the divine. Kenny represents the mortal, flawed world, while the angel is from a perfect, celestial realm. Their relationship often explores this contrast. For example, in some fanfics, Kenny might be envious of the angel's purity, and the angel might be intrigued by Kenny's tenacity in the face of his difficult life.
One common theme is friendship. Despite their differences, they form a bond. Another is the idea of redemption. Kenny might be seen as someone who needs to be redeemed in some way, and the angel could play a role in that.
The theme of discovery is also common. The two characters discover things about each other, about themselves, and about the world around them. The angel might discover the chaos and beauty of the human world through Kenny, and Kenny might discover a new sense of purpose or a different view of the afterlife through his relationship with the angel.
One common theme is friendship. Despite their differences, fanfics often explore how Cartman and Kenny can be friends. Another theme is conflict. Given Cartman's often mean - spirited nature, there's often conflict between them which makes for interesting storylines.
One common theme is friendship development. They might start as just classmates or rivals and gradually become closer friends. For example, a story could show how they overcome their differences over time.
One common theme could be friendship. They might explore how Kenny and Lee build a strong bond and support each other through different situations.
Growth is also a theme. Fanfics might show how Kenny and Kyle grow as individuals while also growing in their relationship with each other. They could learn new things about themselves and each other as the story progresses.
Another theme could be self - discovery. As they interact with each other in the 'kenny x kelly fanfic', they also learn more about themselves. Maybe Kenny discovers his hidden talent for painting because Kelly encourages him to take an art class. And Kelly might realize she has a more sensitive side when Kenny shares his past traumas with her.
Another common theme is growth. Their relationship can be a catalyst for their individual growth. For example, Butters might become more confident through his interactions with Kenny, and Kenny might become more empathetic towards Butters. This is often shown in fanfics through different story arcs.
One common theme is redemption. The broken angel often tries to atone for something or regain its former self.
One common theme is redemption. Angel, being a vampire with a soul, often has a journey of redemption, and Xander can be a part of that journey in the fanfic. For example, Xander might be the one to push Angel further towards the good side.
One common theme is the struggle between good and evil. Since you have an angel representing good and a devil representing evil, there's often a battle of ideologies. Another theme is redemption. Sometimes the devil character is shown to be redeemable through the influence of the angel.
Power and its consequences can be a theme as well. The 'angel of slaughter' is likely to have a great deal of power. Fanfics might explore how this power affects the character, those around them, and the world they exist in. Does the power corrupt? Or can it be used for good despite its violent origin?