Otoko shika inai Kuni no Alice

One day, high school student Arisu suddenly faints and wakes up to find himself in the middle of an intense fight with his best friend Oodate! Confused and disoriented, Arisu is unexpectedly exhilarated by the newfound sensations of his body, which has "developed" according to Oodate's words: “We've done it many times.” To make things stranger, his sister has become his brother, a female idol is now a male idol, and his best friend has turned into his boyfriend. He has apparently been transported to a “world where only men exist.” To return to his original world, Arisu is told that he must “recreate the situation in which he transported,” leading him to repeatedly have sex with Oodate...?

(Source: Gentosha Comics, translated)

Note: Includes 3 extra chapters.