MTL - Rebirth Turn of the Century - Chapter 784 that person

Oosuki Masato is an ordinary high school boy who is magically transported to an alternative world, but for some reason his doting, over-protective mother comes along as well.

Jun Xie was the number one assassin in modern earth. His skills and knowledge in the field of assassination were unparalleled, his accomplishments unprecedented, his reputation terrified the entire underworld. However, during a mission to retrieve a mystical treasure, a mishap occurred…

He is now Jun Moxie, a sixteen year old super level debauchee, sole heir to the declining Jun family. A family of valiant heroes, left with an old grandpa, a crippled uncle and a debauchee as the sole heir! Accepting the world’s criticism and cold stares with a smile, his new journey begins! His life will be carved by his own will! Rise to the top! Evil Monarch Jun Xie!

“This cup I toast to those I’ve killed in my past life. Forgive me, for there is no chance for you to have revenge. Gulp!

This cup I toast to those whose life I will take in my new life. Forgive me, for you are fated to die by my hands. Cheers!”

- Description from novelupdates

In a future timeline, the earth was visited by a species known as the Slarkovs.
Having lost their home planet and in search of a new one, earth was the next habitable planet for them.

Humans and Slarkovs made a deal with each other in return for the Slarkovs living on earth.
The Slarkovs traded their technology and knowledge for a new home.
They were similar to humans except for some of them who had slight differences so fitting into the society wasn't a problem.
Over the years Slarkovs and humans began to mate with one another and reproduce offsprings.
This in turn created a new species known as the mixed-blood.
Centuries later mixedbloods could tap into their bloodline and perform unimaginable feats.

Gustav born into an age where bloodline determines everything, struggles to fit with a useless bloodline.
His bloodline only grants him the ability to change his hair color, destroying his hopes and dreams for a great future.
His fate is turned around when an unexpected situation leads to him finding a system that grants him the power to unlock and upgrade bloodlines by completing quests but he's baffled by two quests with a five-year deadline. Success will grant him unimaginable rewards...
But only one thing awaits him if he fails... Death!

Follow Gustav on his interesting journey filled with unprecedented adventures, danger and death, maybe?

Note:- Return by Death, Harem, few r18 scenes, few disturbing assaults scenes.“I died... and died... and again and again and again,” Alan roared, sitting atop a pile of corpses, arms outstretched, gesturing at the war-torn landscape filled with bodies—all his own, each killed in a different way.“Can I tell you the tale of Alan Fitzgerald?”“How his family betrayed him, how an entire nation hunted him and how he hunted them back.”“All because he wasn’t blessed by those damned twelve gods.”In this world, people who reach the age of 12 will undergo the ceremony called Rite of Ascension, where they'll be blessed by any of the 12 gods.Their blessings determine the future of them.Alane Fitzgerald was the first heir of the Fitzgerald dukedom. Everyone believed that he would be the next chosen champion of the Sun God. Everyone believed that; even Alane believed that.Everyone loved him and cherished him.Until.On his 12th birthday, he undergoes the Rite of Ascension. Something went wrong, clearly wrong. None of the 12 gods didn't choose him; they didn't give him champion blessings, not even common or uncommon blessings. Worse than that, he was marked as a cursed devil.He was thrown into prison by his own parents, mocked by his own younger brother, and finally he was sold as a slave.He wants revenge; he wants to kill everyone who broke him and wants to make them suffer, even the gods who mocked him, but he is powerless.Then he met something dark, which offered him revenge. Gave its own blessings to him.Rather than blessings, it's a curse, yet it'll give him a chance to kill everyone.