"Yuusha" Party ni Sennyuu shita Maou-gun no Assassin ~Kiken-do SSS Class no Mission, Barenai You ni Ganbattetara Onna Yuusha ni Kiniirareta~「勇者」パーティに潜入した魔王軍の暗殺者～危険度ＳＳＳクラスのミッション、バレない様に頑張ってたら女勇者に気に入られた～; "Viper the Stealth," a Master Assassin from the Demon Lord's Army, has Infiltrated the Hero's Party

Tasked by the Demon Lord to "win the Hero's trust," he ruthlessly takes down even his own demon forces, believing "to fool your enemy, you must first fool your friends." But for Nanami, the female Hero whose extraordinary abilities have kept her from a normal life, Viper doesn't just earn her trusthe captures her heart! This is a whimsical fantasy from another world, starring an immoderate assassin and the warrior who loves him.