The joke is Saaya-san is asking him to called her just "Sayaa", without -san, which would imply a more intimate relation. They make the promise with their pinkies, but then he calls her "Oohara-san" (I think it's Oohara, I'm not sure). She scolds him and he finally says "Saaya", to her delight.
Maybe I'll do a complete translation in the future.
Sa...it's ok if it's just now, so make my dream come true, please!Ahahahah... Sa... Saaya-sanIt's a promise! Then let's make it by hooking our little fingers!♥Koyama"San" is not necessary!♥
Really!♥...got it...um... don't stare at me like that...Kyaaaaan!♥ We're hooked up!yubikiri promisedamp washclothGetting called "Saaya" by you, Rikiya, really was my dream!♥Eeh, well then... question 10 for Oohara-san...Yahaaan!♥ My!Wha-... already?!Saaya♥