Ruka got a job at the same karaoke parlor as Kazuya, and the boss loves her so she’s not going anywhere. Ruka believes she can “close the gap” if she’s in close proximity to him in a “Chizuru-free zone” unlike his apartment where she’s right next door.
Having Ruka around reminds him of how he aided in the breaking of Kuri’s heart when Ruka Kuri him to date him. Whether it was right for Kuri to pretend Ruka was his real girlfriend, the fact is he really liked her, and Kazuya is worried the heartbreak will make him distrust or even hate women the rest of his life.
That’s probably selling Kuri too short, but Kuri’s creepy private Twitter account and Kibe’s worries suggest he’s in a deep slump. Flush with cash from his job (and not wanting to anger Ruka by going on a rental date with Chizuru), Kazuya decides to do something he hopes will help cheer his friend up: he pays for Chizuru to go on a rental date…with Kuri.
At first Kuri is simply confused: why would his friend’s girlfriend be going on a date with him? Then he sees how perfect and accommodating Chizuru is and gets self-conscious, to the point he considers Kazuya is playing an elaborate (and cruel) prank. But at some point he realizes he’s having so much fun, it doesn’t matter whether Chizuru is a real or rental date.
Being with someone as lovely as Chizuru restores his faith in women and makes him want a real girlfriend of his own again. That evening Kazuya pops out of the bushes, not to break up the date, but to apologize to Kuri for how things went down with Ruka. He also owns up the fact that he was lying too: Chizuru isn’t his real girlfriend.
While this puts him and Kuri on the same level, that doesn’t stop Kuri from laughing at him and mocking him all the same, which leads to some playful mutual ribbing. However, more than anything Kuri is relieved, and Kazuya’s plan worked, he’s genuinely cheered up. Such is the power of Chizuru. As fo Kuri’s parting question to her—about whether she’d fall for a rental date—Chizuru simply beams as Asakusa glows behind her and says “Who knows?”
Chizuru’s opinion of Kazuya must have improved upon being asked to help him cheer Kuri up. Not only is it proof he doesn’t only ever think of himself and his own gratification, but also that he’s willing to risk embarassing himself if it means owning up to the truth. In this regard, telling Kuri was a practice run for telling their grandmothers, which is still presumably going to happen at some point.
Finally, his request confirms to Chizuru that Kazuya is a guy she can trust to go on a different kind of practice run: Her rental girlfriend colleague Sakurasawa Sumi is just starting out in the business, but has received complaints (and likely poor ratings) for being far too shy.
On their adjacent balconies the next night, she asks him to go on a date with Sumi, trusting he’ll be both kind and impartial. In addition her request, which Kazuya accepts, Chizuru asks about how things are going in his love life completely unbidden, which takes him aback.
All this time she’s been keeping him at arms length, but their talk about his (lack of) progress with Mami looks and awful lot like a legitimate friendship between two people, romance aside. And while it’s late in the game to introduce a fourth girl, I’m looking forward to Takahashi Rie’s take on Sumi.