After five years of harboring unspoken feelings, high-schooler Taiju Ooki is finally ready to confess his love to Yuzuriha Ogawa. Just when Taiju begins his confession however, a blinding green light strikes the Earth and petrifies mankind around the world—turning every single human into stone. Several millennia later, Taiju awakens to find the modern world completely nonexistent, as nature has flourished in the years humanity stood still. Among a stone world of statues, Taiju encounters one other living human: his science-loving friend Senkuu, who has been active for a few months. Taiju learns that Senkuu has developed a grand scheme—to launch the complete revival of civilization with science. Taiju's brawn and Senkuu's brains combine to forge a formidable partnership, and they soon uncover a method to revive those petrified. However, Senkuu's master plan is threatened when his ideologies are challenged by those who awaken. All the while, the reason for mankind's petrification remains unknown.

Senkuu has made it his goal to bring back two million years of human achievement and revive the entirety of those turned to statues. However, one man stands in his way: Tsukasa Shishiou, who believes that only the fittest of those petrified should be revived. As the snow melts and spring approaches, Senkuu and his allies in Ishigami Village finish the preparations for their attack on the Tsukasa Empire. With a reinvented cell phone model now at their disposal, the Kingdom of Science is ready to launch its newest scheme to recruit the sizable numbers of Tsukasa's army to their side. However, it is a race against time; for every day the Kingdom of Science spends perfecting their inventions, the empire rapidly grows in number. Reuniting with old friends and gaining new allies, Senkuu and the Kingdom of Science must stop Tsukasa's forces in order to fulfill their goal of restoring humanity and all its creations. With the two sides each in pursuit of their ideal world, the Stone Wars have now begun!

Tooru Honda has always been fascinated by the story of the Chinese zodiac that her beloved mother told her as a child. However, a sudden family tragedy changes her life, and subsequent circumstances leave her all alone. Tooru is now forced to live in a tent, but little does she know that her temporary home resides on the private property of the esteemed Souma family. Stumbling upon their home one day, she encounters Shigure, an older Souma cousin, and Yuki, the "prince" of her school. Tooru explains that she lives nearby, but the Soumas eventually discover her well-kept secret of being homeless when they see her walking back to her tent one night. Things start to look up for Tooru as they kindly offer to take her in after hearing about her situation. But soon after, she is caught up in a fight between Yuki and his hot-tempered cousin, Kyou. While trying to stop them, she learns that the Souma family has a well-kept secret of their own: whenever they are hugged by a member of the opposite sex, they transform into the animals of the Chinese zodiac. With this new revelation, Tooru will find that living with the Soumas is an unexpected adventure filled with laughter and romance.

A year has passed since Tooru Honda began living in the Souma residence, and she has since created stronger relationships with its inhabitants Shigure, Kyou, and Yuki. She has also grown closer to the rest of the Souma family and has become familiar with their ancestral secret, having helped them with many of their personal issues. The closer Tooru gets, however, the more she begins to realize that their secret holds a darker truth than she first presumed. Summer is approaching and Tooru is invited to spend her days with the Soumas, mainly Kyou and Yuki. Tooru wishes for an easy-going vacation, but her close relationships with the two boys and the rest of the Soumas may prove to cause trouble. As they grow more intimate, their carefree time together is hindered by older hardships and feelings from the past that begin to resurface. The Eternal Banquet also dawns on the members of the zodiac, and they must tend to their duties alongside the unnerving head of the family, Akito Souma. With the banquet approaching and a plethora of feelings to be solved, will Tooru's life with the Soumas remain peaceful, or will she find herself in a situation from which she cannot escape?