Guide to the Perfect Otaku Girlfriend: Roomies and Romance Volume 3 by Rin Murakami

What am I going to do?! Elena overheard Kokoro in my house and now she wants our help cosplaying! I saw the outfit she’s planning to wear and...wow. Why is it so skimpy?! It looks like Kokoro’s going to the event to find a potential boyfriend. That's cool and all, but why do I have to come? Well, I guess she does need someone to watch out for her after what happened last time...

Now Elena and Kokoro have come up with a plan that'll get both of them used to wearing revealing costumes in public: “Let's go to the pool—all three of us!”

That makes sense. Wait...three?!