[Musashi Daichi] Inmu Iseki (Isekai Musume to no Kousetsu Vol.5) [q91]

A buxom female warrior, identified as Leela, stands ready with a sword in the ruins of an ancient fortress, facing a grotesque tentacled monster that claims its corpse will grant eternal life. The creature overwhelms her, using its massive limbs to bind and violate her while boasting of superior virility compared to Grey and threatening dire consequences. The tense, lewd confrontation in the desolate ruins creates a gripping erotic struggle that keeps the reader invested.