Kari Kare!!
Fudanshi Kanata is a repeating his university exams, so his parents get him a private tutor. The tutor, Seiichi, looks exactly like Seijurou, Kanata's favorite character from a BL manga, though personality wise, they're exact opposites. Seiichi promises Kanata if he can meet the conditions, he'll become his personal boyfriend.
Veggie Channel
Average high schooler Vege is a hardcore fudanshi, who runs a live channel where he secretly streams his male classmate in BL-like situations. However, after suddenly receiving a suspicious email, Vege discovers the secret relationship between his population classmate Serizawa and Serizawa's childhood friend Ukyo.
Harukawakun To Yukisensei No Fudanshi Jijo.
Ch.1-4.5: Fudanshi Harukawa's the assistant of his favorite BL mangaka, Fuyuki, a middle-aged man. Despite both men being straight, Harukawa falls for Fuyuki. When Fuyuki asks Harukawa try gay sex with him, Harukawa refuses, until finding out their feelings are the same Ch.5-6: Sed, an incubus who can only seduce men, is caught by exorcist Rodi and gets forcibly reverted to his true, middle-aged form. After seeing this form, Rodi makes a deal to not to exorcise Sed, if Sed has sex with him
Mashita No Fudanshi-kun