Might Gai was supervising his team's training when his eternal rival, Hatake Kakashi, appeared next to him. Kakashi looked half-panicked, and was bleeding from several cuts on his person. To say that the green spandexed jounin was surprised was an understatement. His eternal rival did not often look so….ragged.
"Greetings, my eternal rival," Gai shouted, beaming and flashing his frighteningly flashy teeth. Behind him, Lee was about to copy the movement when Neji and Ten-Ten tackled him.
"Yo." Kakashi said, then took a deep breath. It was against everything he had ever done to ask Gai for help, but he desperately needed it. "Gai, do you think that you and your team could help me in something? Iruka is sick, and I'm substituting his class for the day. But I have no talent with students, and I thought that you, who are so well acquainted with youth, would be able to help give them the learning experience that every not-yet ninja needs." Never let it be said that Kakashi did not know how to get exactly what he needed out of people.
Gai leaped up, tears pouring from his eyes as he struck a heroic pose. "You have come to the right person, my eternal rival! We will be more than happy to help the youth in your care! Lee, Ten-Ten, Neji! To the academy!" The two jounin disappeared in a puff of smoke, leaving the genin to walk quickly to the training yards. What now?
They found the not-yet ninjas sitting starry-eyed on the ground, listening to Gai. Kakashi leaned against a tree, perfectly happy to leave the class in Gai's more capable hands. He wished that Iruka had not made him leave his current copy of Icha Icha at home, for no he had nothing to do. He watched as Gai enlisted Lee, Neji, and Ten-Ten to help show the students how to correctly throw shurikans. Neji seemed particularly absorbed with teaching the Hyuuga in the class how to throw three shurikans at a time. He seemed to be using Lee as her moving target.
The girls seemed fond of Ten-Ten, and they were showing her how well they could stand around and gossip. Lee and Gai had their own small circle of fans, and Kakashi knew Iruka would have their heads if some of his students showed up for class in jumpsuits and bowl cuts. Ah well, such was the price of good behavior. Lee was already teaching them the nice guy pose, and some of them would surely spend several hours scrubbing their teeth to make them shine just so.
Class ended far too quickly, and many students seemed reluctant to leave. Just as reluctant were their instructors, as Lee raced over to Kakashi. "Will Iruka-sensei still be ill tomorrow?" he asked, probably imagining spending the entire day with his new fans.
"I don't know."
"He should rest." Came Gai's voice. The jounin seemed overly worried about Iruka's health at the moment. "The only way for him to stay in the spring of youth is if he recovers fully before returning to the academy." From the looks on Neji and Ten-Ten's faces they whole-heartedly agreed.
"You're probably right. I'll advise him to take tomorrow off, just to rest and recover." Kakashi couldn't wait to tell Iruka that. He was probably doomed.
"Eternal Rival, you should personally make sure it is so!" Gai shouted, throwing an arm around the copy-ninja's shoulders. "Do not worry, for tomorrow Team Gai will assure that the class is taken care of!" With that, the four of them raced into the sunset.
------------------------------- Later
Iruka all but tackled Kakashi when the jounin came home. The fact that his lover was bleeding did nothing to allay Iruka's fears about the day. Kakashi could see the question in Iruka's face, and hurried to reassure him.
"It was fine. They took notes, then I took them out to throw shurikans. That was a little harder, so I went and got Gai and his team. Who, by the way, will be substituting your class tomorrow as well. They all seemed to think you need rest."

In retrospect, Kakashi decided it could have been worse. Iruka was unarmed, and the fever meant he couldn't hit very hard. Besides, eventually Iruka slumped against Kakashi, and the jounin carried him back to bed. Time to obey Gai's orders and make sure Iruka rested. He had the chuunin's best interest in mind, after all. If he didn't, he would never had let Gai substitute the class. That was a sacrifice.