I hope for a plot something like ...
Ruka goes to Kazuya apartment and she see in the trash some papers about "methods to make your crush fall in love for you" with a special method marked with a pen.
It's about a special formula of alcohol and some drugs that the paper said it's 100% success.
She goes mad as she thinks that this is from Kazuya trying to manipulate Chizuru... but, she thinks again and imagine that he will blame her for search in his trash, and after all, he has drop the formula, so he has done the right thing.
But she thinks again... What if she used the formula instead of him? It is a possibility to consider, so she hide the formula.
After check that the apartment is empty he meet a handsome guy that search for Chizuru. He's Umi,
For a moment, Ruka imagine... If she fall in love with him, Kazuya would be devastated and without Chizuru, she will be the number one for Kazuya. She will comfort him.
Ruka interrogates him and after have some clues that he could be interested in a date with Chizuru, she offers a double date.
Kazuya and Chizuru, after be surprised by Ruka that their "friendship hang out" turns into a double date including Uma, she offer drinks and use the formula on Chizuru and Uma drinks in hope of they fall in love under the chemicals and the jealousy of Mizuhara when she (Ruka) kisses Kazuya.
BUT... Chizuru search for a excuse to go out some minutes with Ruka.
After some discussion they enter and...
They find Kazuya and Uma in "bro" mode, Kazuya drinking Chizuru's, both totally drunken, Kazuma complaining about how expensive are rental girlfriends and Uma telling him that real girlfriends are A LOT MORE EXPENSIVE.
Uma - "Once they catch you.... BOOOM... They want a lot of dresses, a car... a house... to be your wife... have children...."
Kazuya - "Oh.... I would love have children with Mizuhara."
Uma - "Wait... The name of your girlfriend... is Ruka, isn't it?"
Kazuya - "Yeap... Ruka wants to have children with me too... BURP"
Uma - "BUUUUUUUUUURP"
Kazuya - "You are a good guy. I wouldn't complait if Chizuru ends with you...."
...
Kazuya - "No... That's a lie... I will complain a lot anyway."
...
Uma - "But Chizuru loves you...."
Kazuya - "...... BWAHAHAHAHAHAHAHAHAA!" - and fade away
That scene with the girls in the background, hearing everything, while Ruka explain Chizuru that it is her fault because are the effects of a "secret formula".
Only to learn at the end, next day, that the formula was from Mini. She discarded it because the real effects are dangerous big booze and it was a hoax from internet.
I would love to see something like this.