TL
R he turns into a mass murderer after his family gets executed and destroys the country.
Afterwards it returns to being happy go lucky slice of life. the revenge plot is only part of the first arc as he kills everyone at the end of it.
Everything in between the things i mention bellow is character building, introducing new characters, or progressing the story while being light hearted for the most part.
First arc ends with everyone in his "family" gets killed off and he turns into a "Demon lord" ( by killing 10.000+ people) resulting in him murdering almost everyone in the country other then the lucky few who escaped his transformation.
He then escapes into the forest, living the as a hermit because of his depression and his demon lord aura/bloodlust scaring everyone to death for a while until he finds a unicorn who is getting attacked by soliders whom he saves out of pitty starting the 2nd arc.
This leads him to leave the forest, return to civilization( in another country )alongside the unicorn disguised as a horse. ( Because barriers can be used to make illusions by bending light....yeah.... )
and a fox who works for a god(there are more then one ) that gave him the power to speak to animals, hide his aura and explaining the skill system in more detail.
Because the gods themselves now fear what he could turn into if he stayed evil as killing people is a good way to get stronger but it also turns you into a mindless monster eventually.
the fact he did NOT turn into one after killing 10.000 people is what makes him scary to them, as a mindless monster is alot less scary then a smart one.
The second arc starts with him setting up a shop with the help off the heirlooms and money from his family and the huge powerboost he got from turning into the demon lord.
after he stopped being a moody little wanker thanks to your friendly neighbourhood prostitutes ( he actually befriends them, not paying for "services").
there is alot of stuff inbetween like for example him saving some orphans who he later on hire to run the store for him because....
The arc ends with him getting a peice of land and turning into a nobel because of his contributions to the country. ( and seducing the princess )
The third arc starts with him saving the only remaining village on his land from a bunch of bandits who turns out to be his own people from other villages who are starving to death caused the land have turned barren from too much salt in the earth.
This arc is all about him restoring the land, city / country building with a lot of worldbuilding and also a few extra members to the harem ( well i guess you have at least one in every arc ).
Because everyone needs a harem right ?
but yeah i did some overarching explanations to the plot but there is alot of minor plot points inbetween and stuff to fill out the story.
its actually not a bad story all in all but its far from perfect, my biggest gripes that i can remember was the fact the story was super slow at times and the generic conplaints that comes with the typical isekai harem mangas.
its abit like "Isekai Tensei Soudouki" in that regard.
