Aa, Ikiteiru tte Subarashii

Called a failure by his adoptive parents, bullied at school, ignored by teachers, high school boy Kurogane Rikuto has nowhere to belong neither at home nor at school. "Life is shit. I guess I'll die." After saying this, he was about to commit suicide by jumping off the school's roof when suddenly all sorts of monsters started appearing from students' smartphones, transforming the school into a hellscape of screaming agony. Goblins, orcs, slimes... Everybody has seen them in games: "small fry monsters." However, humans in the real world, where there is no magic, no special abilities, and no leveling up, are devoured by those "small fries" without any means to retaliate. Rikuto, spared from the incident due to his bullies destroying his phone, seeing the students who bullied him and the teachers dying unsightly deaths and the collapse of order, realizes he does have a desire to survive. Just then, a goblin wielding a club attacks him from behind... Thus begins the survival action tale of one insignificant human driven into extreme circumstances.

(Source: Shueisha, translated)