Zhanxian (Immortal Executioner) - Chapter 536.2: After Thought

A young boy genius, Suo Jia, is a water mage who dreams of being a warrior travelling the great and dangerous trade routes to find his lost father that set off on them before Suo Jia was born. Having to look after his sick mother, Suo Jia manages to find a way to solve all their problems, as well as make a name for himself. He gathers nobility, vast wealth, items of great power, knowledge lost to the ages, and exceptionally talented females around him as he plots and plans – preparing to set off on an epic journey that will go down in history as a new legend. However, will others that depend on his powers so much be willing to let him go on such a dangerous journey so easily?

- Description from Novelupdates

Being able to see into people's past has no real appeal for the teenager this story is about, letting him use it only as amusement and to show off when he was drunk.Never watch into someone's past beyond a superficial level.Never try to find out more than you should.NEVER. EVER. LOOK. INTO. THE. FUTURE.But everything changed the moment he was forced to look into the future, was forced to investigate a murder, and was forced to make the acquaintance of the victim's twin brother('s fists).The more time passed, the more it appeared that the primary reason for this murder wasn't a local problem, but a global one.This single, marred corpse was the beginning of a threat that would shake the world.(MC looses a screw when he enters the prison)BL, first-person view; MC is shuo (perhaps even a reversible couple); love interest falls in love first; both MC and ML are straight, mutual bending, Enemies to Lovers

“When the old gods are forgotten, they do not die—they wait.”In the year 1025, the Viking Age wanes.Iceland bows to Christ. The Althing governs by law. And the gods of old fade to whispers.But in the far Westfjords, something stirs.Vetrulfr, a former Varangian captain and exile, returns from the East with foreign gold, forgotten warcraft, and a hunger no man can name.He comes not in peace, but to raise Ullrsfjörðr from ash and ice; building walls, carving runes, and waging war on behalf of a dying faith.From Reykjavík to Aachen, rumors spread: a ghost walks the North once more. Some call him the son of Ullr. Others, a wolf-cloaked demon.But all will know his name.and when the Valkyries call, he will answer.

The strongest Demon Lord dies, and reincarnates as a human. Not only that, he because of various incidents turns into the hero’s best friend.

Follow his journey as he tries to help the hero escape his fate, and on the sideline to conquer the continent while he’s at it.