[Bashiu Zensen] Onee-Chan ga Daisuki Monsters ~Boku to Youkou ni Natta Onee-Chan~ [SDTLs]

A shy boy's monster-card duels turn carnal when his doting older sister transforms into a voluptuous fox spirit who fights as his partner, absorbing every defeated foe's power with her enormous breasts. Between battles she presses a mysterious card called Heart Gate into his hands, promising that onee-chan will be with him forever — and once he accepts, she smothers him in overwhelming paizuri, teasing that he could never hope to endure real sex. Dominant, doting, and utterly shameless, this fox onee-chan turns an innocent card game into an incestuous match neither sibling wants to end.