Where'd you get that from? (What's your source?) In ch 14 they've just arrived in Osaka and met Shouma. The only girl there are some aunties and Yoshida herself. And I'm pretty sure the girl in ch 13 isn't Yoshina's cousin, but a girl who Kirishima slept with in the past. And that she is kinda nervous since she doesn't want the others to find out she's slept with him before. (Think she's an idol?)
I mean, Kirishima and the cousin did was ride the ferris wheel and talk about Yoshida.
SPOILERS
Kirishima is asking about the truth behind Yoshida's sold kidney.
Here's my source: http://kirishimafansub.net/lector/series/raise-wa-tanin-ga-ii/
Raws? For chapter 13? I only read the raw of chapter 12.3 TT help a girl out?