Time travel shananigans have teen sephiroth in the post Advent. Somehow Cid and Shera end up adopting him.
No oen knows how it happened.
Somewhere along the line though Cid declared that "no fucking snot-nosed kid was being sent back to war and torture"
Sephiroth does not grow up to try to destroy the world. Also while he can cuss like a sailor...he does not because he would like it if his Ma didn't threaten to wash his mouth out.
Sephiroth is...a little emotional, the first time he signs his name as Sephiroth Highwind, and he touches the goggles around his neck gently.
Cid is not gentle persay when he dunks Sephiroth into Aerith's cleasing pool in the church. But daggint...he thinks he adoptd himself a kid and you don't let your adopted kid get used by evil space aliens.
He, Denzel, Marlene and the other kids love racing bikes. (Though Sephiroth is now honor bound to like ships better...)
He's never had his own room before. No cameras...no monitors.
His Ma just sticks her head n once a week to make sure he's kept it clean enough to earn his weekly allowance.