Makiko Nagaoka 
You Were Experienced, I Was Not: Our Dating Story 3rd Date (Light Novel) [EPUB ebook] 

As summer break ends, Ryuto, Runa, and their friends gather to play airsoft, after which our main couple goes on a lovely date in Odaiba! Soon after that, Ryuto enrolls at a cram school for the sake of Runa and his future together. There, he meets Sekiya Shugo—a guy who spent so much time focused on girls in high school that he failed to get into college. He also has a connection to a girl Ryuto knows quite well…

Meanwhile, Runa finds an opportunity to start rebuilding her relationship with her sister. Since Maria is joining the school festival committee, Runa and Ryuto join too. Will Runa and Maria’s relationship improve, or will Maria grow closer to someone else instead?