In the first story, Sasuke challenged Tsunade to a fight because she kissed Naruto's forehead... which he lost. She put a jutsu on him to freeze his sexual desire, much to both his and Naruto's annoyance. The second story is the main one: Team 7 is doing a mission in the forest, and when it gets late, the fireflies come out. Sasuke's allured to Naruto's open enjoyment and kisses him. But afterward, Naruto acts exactly the same. Sasuke confronts him about it and takes him back to his place to show him exactly what that kiss meant.