Marrying the Devil Because I Beat Her in Blackjack

(This story is an "experiment", see auxiliary volume for details) The protagonist joins his school's eerie game club out of boredom, and quickly finds himself playing blackjack with the Devil. She spares his soul after being defeated, but now she's after his freedom and insists that he marries her. Cover art is temporary and belongs to Pepe (ぺぺ) on Pixiv.