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

Tiana and Nick's visit to the casino was only meant to be 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... If only he had some chance, if only he was offered some sliver of power... Then the Survivors would not have seen the last of him yet!