When Gai is made a genin at age seven, Kakashi shows up at his place with a bento box made by him and an offer for a challenge. It's a bit out of character, but Gai's not about to turn down food and a challenge. He'll take that offer enthusiastically.
They end up having a spar in training field two and eating their bento boxes on top of Hokage mountain over looking the village.
While eating his lunch and talking to Kakashi about all of the things he's excited about now that he's officially a genin, Gai can't help but ask why Kakashi asked him for a challenge. It's not something that he has ever done before, and most of the time he says he's too busy for challenges and 'kid stuff' because of his missions and training.
Kakashi doesn't speak immediately. Instead he looks down at his food and picks at the grilled fish. After a while, he looks up at Gai and gives him the best smile he can come up with.
"Because you deserve something good," he responds with fondness. "I tried to think of a good present for your graduation, but I couldn't think of anything that you could use or that you might want. But then i remmembered that you like our challenges and just..."
He waves a hand around the space they're sitting in.
"Hanging out. So i thought it would be a good gift. At least, better than nothing."
Gai can't stop smiling for the rest of the day.
His rival, wanting to get him a gift. Thinking he had no idea what to get him and accidently coming up with the best present he could ever ask for.