Apparently, Disillusioned Adventurers Will Save the World, Vol. 6 (manga) — Masaki Kawakami

Tiana and Nick's visit to the casino was only intended as a way to blow off some steam, but when Tiana runs into a certain wealthy young lady getting taken for a ride by her loser boyfriend, she has a chance to show off and do some good at the same time! Meanwhile, Leon stews in his defeat and imprisonment. But the Survivors haven't seen the last of him yet -- he will grasp at any chance, any slight sliver of power, if it will secure his revenge…