So I've made a Snk OC and I will admit she's pretty much a Mary Sue (like she's strong, fun to be around,I guess good looks). I really want to change her but I just love her so much that I can't. I've tried adding minor details (such as she's a bit mentally crazy and talks to herself, is a bit of a dumb blonde,etc) but she has the whole tragic past thing I cringe at it but I still love because in my opinion it's pretty original. I know this'll be complicated to answer, but how can I fix this? :)
Okay, one thing I need to point out to everyone making SnK OCs:
Having a tragic past is NOT a taboo!!
A very large fraction of people within the walls died due to the breach of Wall Maria, and even more died in the Reclamation Project, which, as we all remember, was actually a government ploy to decrease the population because of food shortages. People were dying within all of the walls because Rose and Sina couldn't support their populations plus that of Maria. The Government literally killed thousands of people because thousands of people were dying anyways. It was a sacrifice to try to alleviate food shortages.
Because there was little food, you can bet the crime rate rose with people trying to steal food, doing whatever they can to feed themselves or their family. People probably were killed by civilians trying to get bread.
Because of all this, no matter what district your character lived in, there was bound to be people dying. It's a really common thing in this show, and if your OC had their whole family die, or if they only had like an uncle die, it's completely plausible. Loads of people had their whole families die, loads of people had friends or distant relatives die.
If you want your OC to have a tragic past in SnK, I say go for it. There is literally no way to go wrong with this show, because it is essentially built on human suffering and death.
Being strong is also not something to worry about. Operating the 3DMG takes incredible strength and dexterity. If your OC is weak, they're not going to be able to operate it and won't be fit for the MIlitary. I say if you deliberately make your character weak in order to bypass some other trait you think is a Sue-Quality, stop right there. If your character is weak, they sure as hell aren't going to be Military Material.
One thing you want to do, however, is equally balance your character's attributes. You don't want a character who is excellent in marks all across the board. If they're incredibly strong, tone it down a notch on the intelligence and reaction times. You don't want to max out your character in all regards.
As long as you don't do that and your character doesn't have physical characteristics that are completely impossible in the SnK realm (Let's say they have cat ears and 4 pairs of wings), then you should be 100% fine.