MTL - House Witch - Chapter 92 91. Horse monkey shochu, transformation

A skilled but unfortunate modern-day assassin was killed in a freak accident. However, he soon found himself summoned to another world by an evil wizard, who had him possess the body of a boy as an experiment. After successfully planning the evil wizard’s downfall, he used the wizard’s body as a springboard to gain influence and power in his new world.

- Description from Novelupdates

An unnamed 34-year-old Japanese NEET is evicted from his home following his parents' death.

Upon some self-introspection, he concludes that his life was ultimately pointless.

Walking down a street he intercepts a speeding truck heading towards a group of teenagers, in an attempt to do something meaningful for once in his life he manages to pull one of them out of harm's way before getting himself in the way of the truck and dying.

Awakening in a baby's body, he realizes he has been reincarnated in a world of sword and sorcery.

He resolves to become successful in his new life, discarding his past identity for his new life as Rudeus Greyrat.

When natural disasters ran rampant, with extreme cold and storms spreading endlessly…When the world mutated, zombies surged like tides, and eerie horrors emerged…When the apocalypse descended, massive Devouring Abysses hundreds of kilometers in diameter began appearing around the globe…When people looked up at the atmospheric cloud layers and saw the slowly emerging corpse of a colossal evil god…From that day, people began to notice that daylight was arriving later and later, until the sun no longer rose, plunging the world into an unending polar night.For survival, on that day, the Apocalypse Radio made its final broadcast to the world:“Everyone, flee eastward—escape to dawn!”…Lin Xian awakened the [Mechanical Heart] ability. He could devour machinery to gain various mysterious skills, scan machines to obtain blueprints for manufacturing, and even use his thoughts to achieve unified control of different machines.Thus, he found a 200-ton heavy gas-powered locomotive, towing specially modified storage, planting, production, medical, and living carriages, and embarked on a 320,000-kilometer journey along the planetary orbital rail—charging eastward toward the dawn!

A tree of 10,000 flowers, the world is the door.
The spells change a lot, but the hearts of the people are unchanged.

- Description from Uukanshu translation