Isekai demo Kagiya-san

One day, a strange request comes to Jinroku Kii, nicknamed "Lock," a freelance locksmith in Japan. The suspicious-looking customer brings him something that looks like something out of a fantasy: to unlock a treasure chest. With his high skill and extensive knowledge, Lock's name quickly becomes known when he takes on a lock-picking job at the request of the otherworldly thieves' guild, Melodia.

(Source: Takarajimasha, translated)