Did the MC really take part in battles?
Idiot makes a huge wall but no opening so let the whole demon horde swarm around instead of being funnelled through a narrow channel by just making a single opening in the wall.
And just 1 massive wall. Great idea, no contingencies for anything if something goes wrong.
No wonder idiot lost everybody in the last life, is being stupid a requirement for reincarnation.
From the start of this story felt like something was off. Now I know it was the idiotic MC, Heck anybody else in that village would have made a far better MC than stupid, stubborn and bird-brain Eric.