In the mysterious future, crystalline organisms called Gems inhabit a world that has been destroyed by six meteors. Each Gem is assigned a role in order to fight against the Lunarians, a species who attacks them in order to shatter their bodies and use them as decorations. Phosphophyllite, also known as Phos, is a young and fragile Gem who dreams of helping their friends in the war effort. Instead, they are told to compile an encyclopedia because of their delicate condition. After begrudgingly embarking on this task, Phos meets Cinnabar, an intelligent gem who has been relegated to patrolling the isolated island at night because of the corrosive poison their body creates. After seeing how unhappy Cinnabar is, Phos decides to find a role that both of the rejected Gems can enjoy. Houseki no Kuni follows Phos' efforts to be useful and protect their fellow Gems. [Written by MAL Rewrite]

On her 16th birthday, Himari Momochi receives a letter stating she has inherited a mansion called the "Momochi House." Having been raised in an orphanage, this mansion is the only thing left of her real family, so Himari pays no mind to the rumors that it may be haunted. Upon entering it, she meets Aoi Nanamori and his companions, Ise and Yukari, who all seem to be squatting in her new home. Although they warn her to leave the house, Himari vows to be the one to make them leave instead. But soon, she is attacked by youkai and finds out that the house sits in the space between the world of the living and the spirit realm. Even more surprising, Aoi was chosen to be the guardian of the house—a position originally meant for Himari. But this great power came with an awful price: Aoi can never leave the mansion, and his existence in the human world has been erased. Ignoring his pleas for her to leave the mansion, Himari promises to help Aoi break the housebound curse as she begins living under the same roof as him.

After her parents were brutally murdered, school girl Sawa was taken into custody by Akai and Kanie, a pair of detectives assigned to her case. Corrupt and immoral, they train the girl to become a weapon, dangling the promise of vengeance in front of the hapless orphan. From celebrities and politicians to influential businessmen, Sawa is tasked with assassinating targets selected arbitrarily by her crooked overseers. She executes every mission without fail, and her distinctive weapon has become infamous among the city's police officers. Physically abused by Akai, who is no more righteous than her victims, Sawa begins to dream of a life unhindered by the shadow of her "guardians." One day, Sawa meets Oburi, a fellow orphan and vigilante. They quickly form a bond born of desperation and disgruntlement at the unjust world, envisioning a future free from the stain of murder.

Kio is just another boring, nice guy with a boring, nice life until he meets a beautiful, curvaceous cat-girl while attending a memorial service for one of his ancestors. Next thing he knows, he's lying in bed with this half-naked beauty next to him! Her name is Eris, and she has come to Earth to learn more about its inhabitants as a representative of the planet Catian. And she's decided to set up shop at Kio's home for her stay on Earth! Unbeknownst to Kio, there are quite a few organizations who will attempt to capture Eris, looking to keep her existence a secret by any means necessary. What's worse is when people around Kio turn out to secretly be a part of those organizations! Kio will have to work hard to keep Eris safe from these shady groups. Things are about to get mysterious, exciting, and most importantly sexy in Asobi ni Iku yo!