BECAUSE JANITOR-SAN IS NOT A HERO

Because Janitor-san Is Not a Hero summary:

A certain girl genius with more power than knowledge accidentally summoned dozens of students and teachers into a dangerous world filled with beasts and magic, but the protagonist isn’t a student or the homeroom teacher… it’s the janitor.
At the time of their summoning, the students and teachers each gained a power formed from their soul, but not the janitor. As the janitor was about to be bestowed with a power that would protect him, his power was forcibly taken from him by an arrogant student. Having gone three years without a contract extension, he failed to get a job after having graduated from a third-rate university. Somehow he is still a contractor at 25 years old and was a janitor for 2 years, with a take-home monthly salary of less than ¥120,000. From a society that rejected him, he was thrust into a world that rejected him. And what janitor-san wished from the Goddess who took pity on him was…