MTL - The Roots of Manga - Chapter 4 Coulson and Iron Man

A 30-year-old NEET is reincarnated into the body of an otaku that choked to death on instant noodles. As he comes to grips with his new life, he realizes that this world is subtly different from Earth. The denizens of this world are far better looking, and this new world also possesses futuristic technology as well as mysterious Yin Yang masters!

He died on the wedding of the girl he had a crush on, after a long and successful career. After convincing Yama to send him back to the world, he decides to fix the areas in which his life went wrong. Realizing the lack of love and romance in his past life, he sets out to conquer the hearts of various women.

- Description from Novelupdates

“Qu Meng’er was born with a silver spoon in her mouth, but her father had tampered with her brakes and ended her life in a car accident.

Mo Chou is the no.1 ranking female assassin in an illusive organization. One day on the way to the organization after completing a mission, she dies. She is shocked when reincarnates into her favorite novel but as a villainess who is the protagonist's step sister and dies a miserable death. She just wants to live a cushy and comfortable life so she decides to completely avoid the red flags aka the main characters and live like a saint (well a saint who is an assassin) But why does she keep stumbling into the main characters especially that infuriating villain and why the heck are they clinging onto her?