My guess is that the Ykuza is his boss. This customer is just some gangster and his boss will show up and show him why you should not mess with a Yakuza. Either the boss or the new harem girl is a daughter of Yakuza boss. But it would be more interesting if it was his boss. Just the story going sideway with him getting in the good side of the Yakuza.
But I would have rather seen a proper progress to the romance. He definitely warming up to the girls. But I really hope that either he goes with the girl behind Yumi since she knows that he loves her Avatar no?
Or just start a proper Harem route somehow