Send My Regards to Kenshiro is a Manga/Manhwa/Manhua in english language, Adult series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.cc fastest updating comic site. The Summary is

The “love, revenge, and slight euphoria” story centers on a young man who swears revenge against the yakuza. He studies the art of the “assassination fist” with all his might, and becomes an adult. But this man who is a genius at his martial art form realizes his techniques cannot actually be used to kill anyone.