Seishirou Amaya liked Azusa Shirayuki. She asked him, "Will you let me lick your penis?" She brings him to an unofficial club that once existed, the Fellatio Research Club, where Seishirou's big dick is sucked to practice fellatio......!!

(Source: Mujin Comics, translated)

Note: Published in Comic Mugen Tensei 2020-12, 2021-07, 2022-02, 06, 2023-01