From INKR: Leng Mo, an indifferent genius 10-year-old boy falls along side a comet into a dreamland by accident. On the planet, he lives with dwarfs and uses his genius might to practice and improve his skills. Just as he has settled down and seems to be living a peaceful life, others' cruel desires to appear
But why would the demon lord summon him? Yeah bcz demon lord was bored wants to fight against a new toy or he was fed up of his immortality and wants to die now.