Well, perhaps in the fanfiction, it's part of a bet between the two. Cartman thinks he can make Kyle so mad that he'll do something really out of character, like kissing him. Kyle, on the other hand, takes the bet to prove Cartman wrong. But when the kiss actually happens, it stirs up a lot of emotions they didn't expect. It could also be a situation where they are under some alien influence. The aliens are studying human emotions and force Kyle and Cartman to kiss to see how the other kids in South Park will react.
In some fanfiction, it could be a dream sequence. Kyle might have a really strange dream where he kisses Cartman. This could be his subconscious dealing with his complex relationship with Cartman - a mix of hatred and an odd sort of friendship. When he wakes up, he's really confused and starts acting differently around Cartman. Or it could be that there's a parallel universe where Kyle and Cartman have different personalities and in that universe, they are in love and the kiss is a natural part of their relationship. However, when they somehow cross over into the normal South Park universe, they have to deal with the shock of their actions.
Chapter 269, "Unexpected Surprise, Xu Ning's Rapid Growth", is the clearest early answer because it turns Xia Hong's situation into a concrete plot event. The setup is Traveling from Wushuang to Wuyuan, one must pass through Jing Valley..., but the pressure keeps building through Upon reaching the two locations, Xia Hong paused quietly for a....
Chapter 217, "Hesitation, Departure, and Sending Word (Part 3)", is the clearest early answer because it pushes Great Xia into a new phase or setting. Early on, Xia Hong could see through Luo Cheng's thoughts with a glance and.... By the end, Leading the position of the alliance hierarch in Longyou for nearly....
Chapter 274, "Weakness and Strength, the Final Battle Begins (Part 3)", is the clearest early answer because the buildup finally cashes out in a real clash. It opens with The broad sword slammed into the great saber, Peng Bo, who was... and closes on In internal competitions, neither side needed to give it their all.. The key payoff is that the danger stops being abstract and the conflict around power growth becomes immediate, forcing the surrounding cast to react under pressure.
Chapter 310, "The Leader Is Still the Best, The Consequences of Losing the Bet", is the clearest early answer because it turns Li Xuanling's situation into a concrete plot event. The chapter gives readers a real answer by opening on You should be very clear about the consequence of losing a gamble,... and ending on Do you really think that last night I was able to lead an army to....
Chapter 210, "Hong Yu, Beehive, Observation", is the clearest early answer because it turns Hong Yu's situation into a concrete plot event. A useful checkpoint is the way the scene starts with Hearing Xia Hong's answer, Luo Ming immediately showed a smile on his... and follows through with Seeing Luo Ming walk to the base of the giant stone, he tapped a....
Chapter 280, "The Vanished Beast Tide and Tenfold Marching Speed", is the clearest early answer because it turns Mirror Valley's situation into a concrete plot event. The chapter turns that into something concrete by moving from Second Year of Great Xia, June 9th More than half an hour into the... to Around the bonfire were hundreds of people, forging iron, driving....
Chapter 234, "Probing, Arrangements, and Hou Hu’s Confidence", is the clearest early answer because it turns Xia Hong's situation into a concrete plot event. The chapter turns that into something concrete by moving from The strength of Zhaoyang, which challenges the status of Long... to Beehive took a more direct approach, building the station underground....
Chapter 213, "Long Mountain News, Ecstasy, and Riot (Part 3)", is the clearest early answer because it turns Luo Ming's situation into a concrete plot event. The chapter gives readers a real answer by opening on This is what a clever person does! and ending on There were seven people in the cave; those who planned to attack him.... In story terms, the chapter exposes hidden motives around Luo Ming, so readers can finally see how the conspiracy layer of the plot is actually moving.
Chapter 287, "Cloud Dragon Army's First Battle, Zhou Yuan's Bloody Struggle, Decisive Victory and Unexpected Windfall (Part 3)", is the clearest early answer because the buildup finally cashes out in a real clash. Early on, The problem is, they still can't make any counterattacks.. By the end, The banner flapped wildly in the battlefield wind, and the Cloud Jiao....
Chapter 218, "Departure, Sending a Letter, Killing", is the clearest early answer because it pushes Ice Abyss into a new phase or setting. The setup is Long Mountain is located more than fifty kilometers to the west of..., but the pressure keeps building through Fifty kilometers might not sound like much..