For a crossover with 'Sailor Moon', Sailor Moon herself would be a natural choice. Her ability to fight evil and her kind heart would make her fit right in. She could team up with Nanami and Tomoe to fight against a new threat that combines the dark forces from both the Sailor Moon and Kamisama Kiss universes. The other Sailor Scouts could also be involved, each bringing their own unique powers.
In a crossover with 'Naruto', Naruto himself would be a great addition. His positive and determined attitude could contrast with Tomoe's more reserved nature. And his powerful ninja skills could come in handy when facing some of the demons in the Kamisama Kiss world. Sakura could also be there, and she might bond with Nanami over their strong wills.
If it was a crossover with 'Fullmetal Alchemist', Edward Elric would be an interesting character. His knowledge of alchemy and his search for the Philosopher's Stone could somehow tie into the magic in the Kamisama Kiss world. Alphonse could also be included, and the gentle giant could form an unlikely friendship with some of the yokai in Kamisama Kiss.
Chapter 700, "As long as the money is in place, I am willing to do anything!", is the clearest early answer because it turns Miss Fu's situation into a concrete plot event. It opens with The official Weibo account of 'Doomsday Beehive' fell in a second,...
Chapter 849, "Observing Fate Through Meridians", is the clearest early answer because it turns Meridians Gu Qiang's situation into a concrete plot event.
If you want the clearest chapter reference, go to Chapter 2. Early on, On the top floor of the Financial Building, a gathering of dark clouds...; later, the chapter leans on How dare Jiang Li hang up his phone?.
Chapter 923, "Eight-legged essay?!", is the clearest early answer because it turns Take Miss Rong's situation into a concrete plot event. Early on, I just went to her house for a meal, even if my relationship with my....
Chapter 705, "Is She Her Own Destined Noble Person?!", is the clearest early answer because it turns Chen's situation into a concrete plot event. The chapter turns that into something concrete by moving from He Wen was made to laugh by Bai Lu.
Chapter 866, "Why don't you die in his place?!", is the clearest early answer because it turns Chen Nanyu's situation into a concrete plot event. It opens with In Shuiyun Temple, Changqing silently watched everything happening in...
Chapter 875, "Isn't That Xu Mei's View?", is the clearest early answer because it turns Jiang Mingchuan's situation into a concrete plot event. It opens with In the information network of the three people, Lu Yafei and Wan Jia...
Chapter 544, "I Shouldn't Have Stopped You from Pursuing Shang Shaojing Back Then", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. Early on, [Hahaha, I'm laughing my head off, how come I never knew Miss Zhuola....
Chapter 938, "When Did the River Moon First Illuminate People? [Extra · River Moon Chapter]", is the clearest early answer because it turns Jiang Yan's situation into a concrete plot event.
Chapter 687, "How Did She Die Again?", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. Early on, In the process of pursuing the Protagonist Group, she gradually came.... By the end, I'm busy here;