First, decide which two universes or characters you want to cross over. For the 'big boss crossover fanfic', you need to choose a world that would make an interesting contrast or combination with Big Boss's own world. Then, come up with a basic plot idea, like a common enemy or a shared goal.
You should also research both the Big Boss character and the elements of the other crossover part. If it's a crossover with a science - fiction series, learn about their technology, society, etc. This will help you write more believable interactions. For example, if it's a crossover with Star Trek, understand how the Federation operates. After that, create your main characters' voices. Big Boss has a very distinct personality, so make sure to keep that intact while also allowing for growth and change in the new situation. And start writing, don't worry too much about making it perfect at first.
Begin with a hook. Maybe start with Big Boss in a completely unexpected situation that is related to the crossover. For instance, if it's a crossover with a fantasy world, start with Big Boss waking up in a magical forest surrounded by strange creatures. This will immediately draw the reader in. Then, gradually introduce the rules and elements of the new world as Big Boss discovers them. As you write, keep in mind the motivations of Big Boss and how they might be affected by the new environment and characters he meets.
Chapter 239, "Changing Situation, Great Xia Special Envoy", is the clearest early answer because it turns Pingxi Plain's situation into a concrete plot event. The setup is From the sudden outburst of violence in Long Mountain a day before..., but the pressure keeps building through Moreover, due to the sensitive point of the alliance's breakdown,....
Chapter 225, "Council at Long Mountain, Li Xuanling's Decisive Action (Part 2)", is the clearest early answer because it turns Li Xuanyan's situation into a concrete plot event. A useful checkpoint is the way the scene starts with What Fourth Brother said makes sense, I agree too." In fact, in Li... and follows through with Bring along Chen Yingyuan and Peng Bo, first capturing Yucheng, then....
Chapter 202, "Worthless as Chickens and Dogs, Four Clans Bow Their Heads", is the clearest early answer because it turns Great Xia's situation into a concrete plot event. Early on, Alright, you can stay here tonight!" Xu An led Xiang Liang to the.... By the end, The issue was that among these one hundred and fifty people, nearly....
Chapter 153, "Terrifying Colors in the Dense Forest, Mirror Immortal Gu Shadow", is the clearest early answer because it turns Great Xia Camp's situation into a concrete plot event. Early on, But the problem is, why aren't they afraid of the solidified fire oil.... By the end, Quickly scanning with his peripheral vision, Xia Hong seized an....
Chapter 150, "Green Bamboo Fence and Marking Stone, Expanding Territory", is the clearest early answer because it turns Xia Hong's situation into a concrete plot event. The setup is Seeing that there was still more than half of the beast blood left in..., but the pressure keeps building through Xia Hong remained in the room alone, continuing to pour the beast....
Chapter 194, "A Tragic Scene, Ice Skin Jade Bone, Xia Hong's True Strength", is the clearest early answer because it turns Xia Hong's situation into a concrete plot event. Early on, The people who had just scattered and fled didn't get far before.... By the end, On Xia Hong's side, he began his assault..
Chapter 170, "Camp Integration, Territory Rapid Expansion (Part 2)", is the clearest early answer because it turns Xia Chuan's situation into a concrete plot event. The chapter turns that into something concrete by moving from As expected of a giant camp, the number of people in the Logging... to The top leaders, He Yuanhun and Yuwen Hu, only needed to oversee the....
Chapter 167, "Snatching the Mirror, He Yuanhun's Confidence", is the clearest early answer because it turns Xia Hong's situation into a concrete plot event. The setup is How about you surrender now and come back with me to the Great Xia..., but the pressure keeps building through Then I can listen to you explain slowly, how about that?" In the....
Chapter 166, "The Defenseless Mirror Immortal", is the clearest early answer because it turns Great Xia's situation into a concrete plot event. The chapter gives readers a real answer by opening on Xia Hong, my leader, among our three thousand people, none have paid... and ending on Moreover, if He Yuanhun wins, it's a dead end for us all..
Chapter 205, "The Director Emerges, Treasure Presentation Opportunity (3)", is the clearest early answer because Xu Ning gets a payoff that changes the stakes. Early on, Leader, this must be the Great Xia Leader..." Xiang Liang looked at.... By the end, Who is this person?" As Yuwen Dao climbed the stairs with the four,....