Kono Sankaku Love Come wa Shiawase ni Naru Gime ga Aru.

"What do you like about Reira so much?" Tenma Yashiro, an ordinary high school boy, accidentally discovers that Rinka, a cool beauty in his class, is in love with his childhood friend, Reira Tsubaki, a beautiful and innocent girl. Tenma then helps Rinka become friends with Reira, but... "If Yashiro-