After being her sensei for so long, he was more like an older brother. He was there for help, he was there for guidance. He was there for support. He was there for comfort. He was there for good fun and all those laughs to be had. He was there.
When that line was crossed, neither knew.
Maybe it was when he went and helped her pick out formal attire at the Jounin Commemorative Ball. Maybe that one night, he came home injured and she tended to his wounds as she saw him barely conscious and bleeding during a surprise visit. Maybe with all the, "really close teacher-student bonding" jokes they would get when see out in public where neither denied the kidding accusations. Or maybe it was those late nights under the dark sky with a blanket of wispy clouds and sheets made of stars over them, whispering stories of their past to each other in their slightly buzzed haze.
Whatever the case, they broke the harshest Village rule.
This is a story of the second Forbidden Love; the two loves that one should never breach in Konohagakure, Man to Man and Teacher to Student. This was forbidden in many other villages within the nations, but was most religiously upheld by this particular village where many Genin have grown into great Shinobi's.
This is the battle of love between Shinobi teacher and disciple against the strict brutality opposing them.
This is the tale... of Hatake Kakashi and Haruno Sakura.