Haunted by dark memories, Kazahana Koyuki was extremely avoidant about returning to the Land of Snow.
Ultimately, after being cajoled by her agent and Sandayu Asama, she returned to the Land of Snow.
Then, the cliché villain Kazahana Dōtō appeared—Kazahana Koyuki's uncle—who sought to uncover the secret treasure of the Land of Snow.
Since the key to that treasure was in Kazahana Koyuki's possession, Kazahana Dōtō sent his men to attack them.
In the end, with the help of Kakashi's team, Kazahana Koyuki successfully resolved her inner turmoil.
Naruto, with the collective effort of everyone, defeated the usurper Kazahana Dōtō, and ultimately, Kazahana Koyuki became the Daimyo of the Land of Snow.
That was the overt plot of that theatrical film.
In reality, there was also a hidden subplot.
Ten years before the story began, Kazahana Dōtō had rebelled, betraying Kazahana Koyuki's father.
Kakashi had participated in that mission as well, but unfortunately, it had failed.
They were held back by the Snow Ninja of the Land of Snow and were unable to avert the tragedy.
Only Kazahana Koyuki and the loyal royal retainer Sandayu Asama managed to escape the Land of Snow.
This event became the knot in Kazahana Koyuki's heart that kept her from returning to her homeland.
"I'm going with Kakashi?"
Shimizu looked at Hiruzen Sarutobi, who was smoking in his office.
"No, you will lead the team this time. Form a temporary squad and take three other ninja with you."
Hiruzen Sarutobi took a puff of his pipe.
Shimizu's presence in the village created too much uncertainty; he needed to get him out for a while.
During this time, he would prepare Jiraiya and Tsunade mentally for the Hokage Selection.
"The three ninja are Guren, Izumi, and... Itachi."
A sharp glint appeared in Hiruzen Sarutobi's eyes.