Tonari no Kashiwagi-san - Vol. 6 Ch. 41

[MangaDex]

 

[etriuswimbleton]

for a girl as indecisive as Kashiwagi, I guess the author feels like they needed something as necessary as a love rival to push her to respond to Yuuto's feelings.

 

[PsychoTheRabbit]

People keep thinking is Kotori fault... Yuuto confessed twice is true. But thats it. He hasnt put any effort to leave the friend zone at all.
Also, i dont like the idea of a possible rival. Not when the mc is already so frustrating. Yeh, each chapter makes me feel i should really had call it when Kazuki and Sayaka had their happy moment.