With the assassination of the Mizukage and an unavoidable war between Kumo and Iwa there was no way Konoha would survive losing the Uchiha clan. Instead, Itachi would take over as the head of the clan by force. It was a futile effort, though, as the war with Kiri began and his brother's generation got caught right in the middle of it.
A single decision set in motion events that Konoha wasn't ready for and two boys that never should have come in contact bonded over a reminder. They weren't ready for a Soul of Lightning to bond with the Will of Fire, or for one of their strongest to get past his guilt, or for a love that couldn't be allowed to blossom between a purple flower and cobalt lightning.
Upon graduating from the Academy the students are divided into groups of three, however, there are two exceptions that require an occasional group of four. Number 1: an extra student. Number 2: a precaution against a lintvern, someone who can use their own soul as a source of power, because a soul can never hurt a loved one and a teammate is a loved one.