Kendoubu Shushou de Osananajimi: Determination
18 parts Ongoing MatureBased on doujin Kendoubu Shushou de Osananajimi no Bijin de Tsuyoi Boku no Kanojo ga, Charao ni Assari Otosareru Wake ga Nai, or in English, it was called My Childhood Crush, the Fierce and Beautiful Kendo Club Captain, Would Never Fall for a Fuckboy (Well, that was a very long-ass title).
Takumi Matsuzaki is a member of his school's kendo club. He has a girlfriend named Kaori Sakura, who is also the club captain. Both of them have been childhood friends since elementary school. It is Kaori who introduces Takumi to the kendo world.
One day, Kaori is blackmailed by a student named Yuusuke, using the video of Takumi's underage drinking. He threatened her to report that unless she had become his lover for a week, and he deleted said video. During that time, Kaori always avoids Takumi, inadvertently severing their relationship.
Could Kaori manage to end her "affair" with Yuusuke and repair her relationship with Takumi?
Fun fact: This is the FIRST NTR doujin I read and the one who introduced me to that godforsaken, cursed, and vile genre/tag. Of course, I read it accidentally, and it scarred me so much that I was even afraid to glimpse it (yep, that's right). This doujin made me hate the story with strong-willed martial artist FMC being a victim. Luckily, I overcame my fear by force-reading it (Of course, I must cleanse myself after that by reading several manga). By overcoming my fear, I could use that doujin as my inspiration to write anti-NTR fanfic.