Noctis:
He’d be asleep when it first happens, and not notice the many small braids until someone points it out to him after they get out of the car to all stretch their legs.
The braids would be small and precise. Almost unnoticeable until you were standing right next to him.
He’d track down his S/O and wrap his arms around them from behind, and rest his chin on their head.
They’d let him hem and haw, playfully complaining about the braids. They’d tell him to shush and say it was for falling asleep on their lap in the car. “My legs fell asleep because of you.”
He wouldn’t really mind. In fact, he’d actually be a little surprise in the amount of work the small braids must have taken.
His S/O would never admit it, but his hair was so fine and soft that wrangling the soft strands into the braids had been super difficult. (Not to mention that his hair had barely been long enough.)
They would then get back into the car and Noctis would soon be laying right back where he was. But this time, though his eyes were closed he was awake. The feeling of their hands in his hair would relax him so much, and this time he would get to enjoy the feeling.
(Though he’d despise how WAVY his hair would be when they’d take out the braids. His S/O would think it’s adorable.)
Prompto:
Like a fussy toddler, he’d not sit STILL long enough to actually finish any of the braids. So his S/O would have to settle for just playing with the strands and twisting them.
His hair would be surprisingly thick to the touch, and he wouldn’t really notice them playing with his hair. (His mind would be watching the landscape around them, or deeply invested in his thoughts.)
His S/O would be so used to having him suddenly move, that their hands become well practiced with feather light touches and pulling their hand just far enough away when he turns his head they don’t accidentally startle him by pulling his hair.
It’d be hilarious to his S/O the day they see him take a selfie, and get the most confused expression on his face when he sees the small beginning of a crown of twisted hair.
They’d make it a game then to see just how much they could alter his hair without him noticing.
He’d eventually catch them, and laugh alongside them at how he’d never noticed them playing with his hair.
Gladiolus:
This would be something he’d be used to after growing up with a younger sibling.
At the first feeling of fingers in his hair, a soft smile would cross his face when he’d look up at his S/O and indulge them.
His S/O would be one of those people that needs their hands busy in order to relax. He on the other hand, just finds the feeling of their fingers in his hair pleasantly relaxing as well. And it’d soon become habit for them at the end of their day to do this with each other.
Sometimes, if they’re on a long car ride together, the braids will also make and appearance because of boredom.
He’d be the one to leave the braids in his hair, finding that it actually keeps his hair off his face better than just styling it backwards.
(Perhaps this is the reason he grows his hair out.)
Ignis:
Imagine his surprise when one day, on the rare chance he drifts off before everyone, he wakes up with his hair in little loosely braided strands. He’s a normally light sleeper, so not waking to someone touching his hair would deeply surprise him.
He’d wonder who, but then realize that the only one closest to him is his S/O, which he’d look at fondly while they slept.
Before they awoke as well, he’d undo the braids in his hair, and manage to get the most of the waves caused by the braids under control. But even with him managing to get his hair into it’s normally style, it’s a lot fluffier than normal.
Actions have meaning with him, so the fact they took the time to place braids in his hair, even if it was just them paying with it, would mean a lot.
As a small form of ‘revenge’, he’d place the tiniest braid in their hair before they woke as well, which when they did wake, they’d leave in the rest of the day.
Imagine Final Fantasy 