[Guido]

A good dramatized episode that faithfully portrays Rena's reaction towards Rina's deceit and betrayal of the latter's trust.

Spoiler:

In regards to Rina's fate previously shown in Tatarigoroshi-hen.....

I do not think that Rena was at fault for that bitch's demise. She was more of Wataganshi -ed.

Stomach cut and intestines disemboweled; nose torn off; 20 nails hammered on her right hand.
That sounds more like the workings of the Sonozaki family or someone else's acknowledged with the Wataganashi methods.

Anyways, returning to topic.....

Spoiler:

Do I wonder if Kasai had a run-in and was scammed by Rina in the past?

His reaction to when Shion asks him if he was tricked before seems like a dead giveaway, however, I may be just too serious overanalyzing a matter trivial to the current issue Rena's facing.

But, when Kasai entered the café, Rina addressed him formally just as she knew him from some time, after Teppei and his debtors left, and Kasai averted his eyesight from her.