Kota
One on his knee from tripping as a kid. Pretty much invisible now.
One or two on his arms, also pretty hard to see. Don't know if the 2nd Break is considered canon, but it's briefly mentioned how Kota and his dad came home all roughed up. Considering that it wouldn't surprise me if he did get some scars from whatever the two where doing.
The main one here is the electricity burns he got from the Nova. They're mostly on his legs, and thanks to how fast God Eaters heal, pretty faded. Soma did have a brief period where he felt guilty about it, but Kota and Alisa got together to stop that before it spiraled.
Doesn't feel much about his scars, he didn't get any on his face, and he can move just fine, so he doesn't see any issue.
Lindow
The arm.
In the anime(say what you will about it, the backstory on the main antagonist, the added characterization for Lindow, and the lore of how everything started was great imo) it's revealed he, Tsubaki, and Sakuya are from the wastelands outside Fenrir's reach.
I liked that addition, so it's part of my headcanon for him.
In line with that, Lindow has some old scars mostly on his torso. Puncture marks, slashes, a burn here, the works. He got into lots of shenanigans out there.
Being a Gen 1 Melee fighter, he earned a few larger scars from the Aragami he's fought. Though those are ironically smaller than the ones he got from the wasteland.
Due to *spoilers* his left eye is slightly faded, only noticable if you know what happened.
Doesn't consider scars to be anything to be ashamed of. Would talk about his scars if asked, although for security reasons he's vague about the arm and eye. Has cracked a few jokes about them.
Sakuya
Not many.
Due to being the youngest out of the three(her and the siblings), she was often kept away from the Bad Times. She had an enter argument with the siblings after becoming a God Eater, as by then Tsubaki was considering.
Later, because she's a sniper, she's usually not close enough to get hit by severe attacks.
Has a small scar on her knuckle from a time she had to fist fight for her survival. Only Lindow and Tsubaki know about it.
After the time skip, she has stretch marks from Ren. Lindow will not leave her alone.
There was a brief time she felt insecure about her scars, but after a talk with Tsubaki she got more confident and became the badass we see in game.
Soma
Pretty much nothing, while he may be the one taking all the hits(being the tank), his regeneration ability is insane so the heavy hits that do hit are gone pretty quickly.
There is one he got from the Nova, it's across his chest and honestly really hard to see due to his skin tone and again, his healing ability. Honestly even the 1st Unit wasn't aware he had it for a while since he's not the type to talk about his physique.
At first he had mixed feelings about it, but by the time the second game rolled around he'd gotten over it. Its not like it hinders his fighting abilities or is really obvious. Only tells the story if he really trusts the other party.
Alisa
(Small trigger warning)
Her scars are all pretty small, and centered around her wrists. They're from her darker days in the hospital. Mostly faded by now, and she doesn't like talking about them.
Aside from those, she's number three for having scars from the Nova. These are small cuts mostly around her sides and largely unnoticeable.
She has mixed feelings about her scars, some days she tries to hide them with makeup, others she doesn't. Sakuya has been helping her feel more confident about herself. So has Kota, results are varied(for him).
Yuu
Most scarred of the 1st Unit.
Honestly my headcanon for him is a mix based off of the few appearances he does have(the various manga, canon events in the game) and of Lenka from the anime. The amount of world building in the anime made my lore addicted brain very happy.
So, while personality wise he's a pretty chill dude, he has a history of recklessness, shenanigans, and other life threatening activities. He's also a survivor from outside of Fenrir, meaning he had to contend with both humans and Aragami to survive.
This resulted in a wide variety of scars all over him, save for the face. Most of them are on his torso and hands. Burn marks, stab wounds, slashes, stitches, and a slightly misshaped pinky from when the top of his finger got sliced off.
Most are old and faded, but some are newer. Because of how he usually wears modest clothing, not many people know the extent of it.
Because he fights packs of Aragami solo, usually ones rarely encountered new scars can crop up if he's not careful. One such scar is on his right arm, a massive bite mark from the Kyuubi.
Honestly could care less about his scars. Would even joke each one told him what not to do. Although he does try to hide them sometimes as he understands normal people might get weird about them.