The Irregular Extra of the Hero's Academy

A young man, who, by hard work and ruthlessness, worked his way to the top, only to find out that he had a traitor in his group; he did succeed in killing that traitor, but he wasn't any better. He died as well.
But his fate seemed to have other plans for him as he was reincarnated in the world of a novel that his girlfriend used to read.
See how he navigates through the world, slowly uncovering the reason behind his reincarnation and the mysterious goddess who made it all possible.
....................................................
What you can expect in the novel: -
- A wholesome novel with some very dark parts within it, so a gray novel.
- There are going to be multiple female leads, so you know what it is: Harem.
- I am not an expert, but I can still write a bit of smut, so you can expect some lemons as well.
- There will be some politics in the story (yeah... no, I don't like it as well, but will have to put it in).
- The MC is going to be an ideal WN MC: Once in an era talented, cold to his enemies, and gentle to his family (he is a bit too ruthless to his enemies, but you get the gist of it, right?)
- The FMLs are not going to be baggage as they would be talented in their own rights.
- Of course, we have a system waifu as well.
.....................................................
This is my first book (...ok, not really), so if you think that there is something that could break your immersion or any other error, please point it out in the comments!