[Sayoyuri Hako (Sayoyuri)] Mahou Shoujo Akushoku ~Futanari Kaizou Maryoku Sakusei~ (SCANMTL)

A magical girl is seized by writhing tentacles that corrupt her body, awaken a powerful futani form, and drain her magic through increasingly intimate encounters. Her enlarged breasts and tentacles strain against her damaged uniform while another magical girl eagerly takes her turn, urging her partner to surrender every last drop of power. What begins as a sudden supernatural assault becomes a mutual ritual of transformation, possession, and escalating surrender.