There are numerous titles featuring "Assassin" in the genre, such as The World's Finest Assassin Gets Reincarnated in Another World as an Aristocrat .
Many sites claiming to offer "Free Download" links for books, comics, or games are fronts for distributing malicious software (viruses, ransomware, spyware).
If you can provide more details, I can help you find a safe and legal way to access it. Specifically: Who is the author?
Authors often release the first volume of a series for free on platforms like Amazon Kindle or Smashwords to build an audience. Identifying "Assassin's Volume"
These sites often require you to create an account, entering personal information or credit card details, which can lead to identity theft.