Death March kara Hajimaru Isekai Kyusoukyoku (WN) - Book 17 - 17-12. Changing World

Untolerated by heaven, a boy was restricted by the most powerful spell.

He accidentally acquired a painting inhabited by nine souls that claimed to be immortal.

Then, the legend of a strong young man who violated heavenly principles against the course of nature began.

- Description from Novelupdates

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?

Your meridians cannot be cultivated? It’s ok! There are Crazy Leveling System, do missions, kill monsters, swallow other people’s spiritual power, make pills or forge weapon, participate in big battle, you can gain experience!

When she woke up again, she found herself become a peasant’s wife…