Rentt Faina, a 25-year-old adventurer, has been hacking away at monsters for a decade. Without much talent for the job, Rentt finds himself stuck hunting slimes and goblins for meager amounts of coin every day. Little does he know, all this is about to change when he comes across a seemingly undiscovered path in the Water Moon Dungeon. What awaits him at the end of the path, however, is neither treasure nor riches, but a legendary dragon that wastes no time swallowing him whole! Waking up a short time later, Rentt finds himself not quite dead, but not very alive either―He is nothing more than a pile of bones! Armed with nothing but his trusty sword, tool belt, and ghoulish new looks, Rentt sets off on his quest as a newly reborn skeleton to achieve Existential Evolution, hoping to one day return to civilization with a more human form. Will Rentt succeed, or will the dungeon consume him for the rest of his un-death...?

After his high school graduation, Yuuki Wakura realizes it has been five years since his sister's disappearance during a "Mato disaster." Throughout Japan, mysterious entrances have opened to a dimension called "Mato"—a demonic metropolis filled with disastrous monsters known as the "Shuuki" that threaten the safety of humans. However, a new hope arose, as the discovery of a Mato fruit that grants supernatural abilities exclusively to women allowed them to fight against the Shuuki. Due to this, a new matriarchal government was formed, establishing a female organization called the Anti-Demon Corps, which caused men to fall to the bottom of society. When Yuuki suddenly finds himself in Mato, he is unable to escape on his own. But just as he anticipates a gruesome end by the Shuuki, a girl in a militia outfit appears and protects him. As the chief of the Seventh Unit of the Anti-Demon Corps, Kyouka Uzen is ambitious yet devalued by her own peers due to her power being deemed unusual. Now in a life-or-death situation, Kyouka takes the opportunity to find out the true potential of her superpower by using Yuuki: in order to defeat the Shuuki, he has to become her slave.

Jun Shirasaki and the Jinguuji sisters are childhood friends and neighbors. When Jun's first girlfriend, the older sister Ryuumi, breaks up with him, she says something that complicates the three people's relationship, their first loves, and their romance—?

Duke Fleed is a survivor of the Fleed Planet who is escaped to the Earth, onboard a mysterious "spaceship", where is raised by Dr. Umon as his adoptive son, and known as Daisuke Umon. Years after his arrival, he's faced with the threat of King Vega and his army, who want to conquer the Earth. With his friends Koji and Hikaru (and later his younger sister Maria Grace), Duke decides to fight back using his best weapon - the almighty Grendizer.