The Magic in this Other World is Too Far Behind! Volume 4 oleh Gamei Hitsuji

Suimei finally has his base set up, new housemate and all, and is primed to devote himself to his research in trying to find a way back home. But things are never that simple for our hard-luck anti-hero from another world. There’s still a shadow on the loose in the city and an unfinished duel with a real hero to settle, but to make matters worse, someone new seems to have taken an interest in Suimei and his affairs. Meanwhile, Reiji and the others continue their own quest to save the world, which may take an unexpected turn.