Sword Art Online world. It followed the exact plot with the exact same events as the original anime, only with the MC replacing the role of Kirito who just fell to a background character. I love SAO, I read all the novels and then watched the anime when it came out, but I'm not reading a different story just to reread what I already know and love. The only difference was that Akahiba, or whatever his name was - I'm not googling it just for reference - wasn't defeated until the 100th floor.
MC turns from a 17 year old anorexic guy into a 14 year old "adorable" loli. Tells the parents and they accept it as it is the most normal thing in the world.
Afterwards, dad proceeds to pat her (him) on the head and she (he) goes "daddy's hand... so comfortable, " before reminiscing that this was the same hand that beat him until he was coughing up blood on the floor for not getting dad a glass of water. Don't forget, he's supposed to be a 17 year boy inside. I want to point out so many things wrong with this, but I'll just stick with my original term for it, sickening.
Next, our 17 y/o boy turned anime loli with serious daddy issues and a re****ation in mental growth, is kidnapped by someone is became/was already a goddess or some crap but is actually her (his) servant. The whole scene up to it is absolutely rubbish, where she is sexually assaulted, the guy? Even saying he fingered her when she was unconscious, and taken physical advantage of because she is a strong weak as a four y/o child. The whole scene was incomprehensible because the author constantly changed scenes from one paragraph to the next.
After suddenly becoming her servant, the MC has the goddess/slave stick a dildo up her arse and leave it there. Because author wants MC to be stronger so he has her turn into a massive sad*** momentarily before regretting what she did. Completely out of character and off putting.
MC then gets a system, which displays her (his) stats. The reading for being so weak is her (his) strength value is at 1. Because of this, she (he) is as weak as a chicken and constantly gets sexually harassed/assaulted. She protests to not sexually harass her (him) but then says "please... don't, or... I will start to like it" with teary eyes... sickening.
She (he) gets free points to increase her (his) stats, yet every time she puts them into intelligence. Despite "becoming more smart" she is still sexually harassed because she still isn't smart enough to think "if I put some points in strength, I wouldn't be so weak everyone can take sexual advantage over me at their own convenience."
Other characters are also constantly inconsistent and change completely depending on the story.
MC is esintially saitama with a different name with a little more seriousness in background yet his personality is laid back and sometimes (seemingly) oblivious to certain scenarios. He casually runs into a crab monster while looking for crab for dinner and one punches it to death before taking it home to cook (A mixture of a scenario and familiar monster here you may recall from OPM)
Second main girl, after his sister, is a battle maniac who practically chases the MC down begging to be his apprentice. Sound familiar? You bet it does. She's a female, human Genos. She even forces MC to "spar" with her that plays out pretty much exactly like the spar between Saitama and Genoa in OPM.
The monsters, called Unknown, are designated into several different classification tiers based on how much damage they can cause. Ranging from district level, to city level etc...
A bunch of men with black hair (dyed black, as everyone in the world other than the MC has a superpower which shows on their hair colour so no one has black hair anymore) cause a riot and want to kill a big shot for their own bullsh*t reason. This is essentially the bald men group from OPM who rioted because they didn't want to work.
The MC has a massive shampoo complex where he is severely obsessed with it, a play that can be interpreted as "he is afraid of going bald"...
The number 1 "hero" hasn't been heard from and is presumed missing to the public *cough* Blast *cough*
Seriously, do I need to go on here? I think you should get what I mean by now.