The Eminence in Shadow, Vol. 13 (manga)

Cid and Beta have arrived at one of the last places the aspiring shadowbroker wanted to go-his former home world, Earth. Or what's left of it, at least. Why's everything in ruins anyway. It doesn't really matter, because Cid has a bigger problem: If Beta works out that his vaunted Shadow Wisdom is all normal stuff any earthling would know, he'll look seriously uncool. He's gotta find a way back to his rad isekai fantasy life while she's still in the dark, but little does he realize that his boring old planet's got some brand-new thrills.