Personal headcanon on how Kakashi started wearing the mask. Yes, I am aware that we see him with the mask before the academy. Very short. Not even two pages. Cross posted on ao3.
"Dad. I'm not letting you make me late. Let's go."
Sakumo tried not to laugh at his son. He was just so cute, trying to act all adult. If only he were adult enough to try to get along with the other kids. Sakumo could almost hear the "but dad, they're so annoying," in response. Hopefully the academy would help him make some friends. Kakashi could definitely use some people to keep him company, now that Sakumo would be taking more missions. With the threat of war hanging over the village, it was inevitable that the Hokage would be less lenient in granting him leave. He regretted that there wouldn't be as much time spent with his small family, but war was war, and the he was the White Fang. Konoha needed him. He wouldn't be home as often, but that didn't mean he would stop being a parent— and parents made their children eat before leaving in the morning.
"You're not leaving until you eat. We still have thirty minutes, but if you're really that worried, grab some something you can eat on the way." Kakashi snatched an apple off the counter and led the way out the door. Sakumo followed, and tried to remember what his first day had been like. Ah! That's right. He knew he was forgetting something! Can't send your son off to school without the obligatory lecture.
"Now, Kakashi, I want you to respect your sensei, okay? No back-talk, and no sass, got it?"
"Yeah, yeah, I-"
"And you be nice to your classmates!"
"Bu-"
"I don't care how annoying they are, be nice to them. Oh, also, no starting fights, but that's a given. No breaking noses. Don't use deadly force. Pay attention in class. Knowledge is just as important than taijutsu and ninjutsu, got it? And make sure you eat the lunch I packed. The academy cafeteria may seem cool, but this is full of nutrients that help you get stronger. You can't be a ninja if you're not strong. Don't overextend yourself— Kakashi?" Kakashi had stopped walking and was staring at his half-eaten apple.
"What's wrong?" He didn't reply, just handed over the apple. Sakumo turned it over, looking for the problem. The apple looked fine to him. "Let's go, you don't wanna be late, do you?" When Kakashi still didn't move, Sakumo crouched in front of him.
"It's okay to be nervous. It's the first day, after all."
Kakashi took offense to that. "I'm not nervous!"
That was when Sakumo saw the problem, and couldn't help but laugh—there was a gap in Kakashi's teeth.
"Hey, your first tooth! You're growing up!" Apparently, Kakashi didn't appreciate that, because he scowled.
"No, it means I look like a little kid! Only little kids have missing teeth. I can't show up at the academy like this." With that, Kakashi turned around stomped in the opposite direction. Sakumo was about to protest when he saw that he was only going to the shore of a lake they passed to look at his reflection.
"Dad. How do I put it back?" Kakashi looked so forlorn, and Sakumo just needed to do something, he couldn't take that look from his son.
"You can't, but…" Sakumo checked his wristwatch, and, deciding that there was just enough time, grabbed Kakashi by the wrist and started walking toward the shopping district. "I have an idea."
Sakumo's idea seemed brilliant until they reached the mask shop and found out that they didn't carry any half masks, only masks that covered the whole face, which were not allowed at the academy. (As if he would let his son walk around in public with one of those on). He was about to apologize to Kakashi when a sock shop caught his eye. He quickly walked over and bought the biggest pair of socks available. They were now running a bit short on time, so they took to the roofs to avoid the crowds on the street. When they were once again on their way to the academy, he took out his tanto, charged it with chakra and cut the sock, leaving behind a tube of stretchy black cloth. Kakashi stared in awe. He rarely got to see his dad using ninja skills or tools, even though he begged and begged.
"Okay Kakashi, let me slip this over your head," Sakumo told him. Looking a little skeptical, Kakashi inclined his head toward his father and let him tug the sock down until it covered his nose, mouth, chin, and neck. On the rest of the way there, he kept glancing at himself in every window they passed. Sakumo smiled. It seemed Kakashi liked the mask. It was cute that he was missing a tooth, but it was even cuter that he was so bugged by it. Of course, even though Kakashi had escaped the embarrassment of a missing tooth, he couldn't let him escape the embarrassment of a hug from his dad in public.
Three years later, Kakashi keeps only two reminders of his father. The tanto brings memories of his father's blood, staining the floor (and the knees of Kakashi's pants where he had knelt, shaking, by the body). It reminds him that he can never even begin forgive his father. The mask… the mask means that maybe, he already has.
Tell me what you thought!