In the latter half of 21st century, humans leave the Earth and begin to live in space. In order to adapt to the environment in space and deal with the hostile aliens in Jupiter, genetically engineered children called "Princes" are artificially raised and trained to be pilots of armed robots "AHSMB (Advanced High Standard Multipurpose Battle Device). This is a story about one of the teenage "Princes," Hitachi O Izuru, who studies in an academic city Grandzehle. (Source: MAL News)

The story begins when high school student Kazuki Muto is killed one night saving a mysterious girl from a monster, only to wake up in his school dorm, believing it to have been a dream; however, he soon finds out that dream wasn't a dream at all when a giant serpentine monster attacks him and his sister. Tokiko Tsumura, the girl he saved, explains that the monster is a homunculus. Kazuki had been attacked and killed by it when he was rescuing her; however, she, feeling responsible for him, revived him by placing a Kakugane medallion in his chest, serving as a replacement heart. The Kakugane, as Tokiko explains, is an alchemical device that, when activated, takes a certain form based on the Kakugane's user, forming a unique Buso Renkin. The Buso Renkin is the only thing that can destroy a homunculus monster. Using this, Kazuki creates his own Buso Renkin (the "Sunlight Heart," a huge lance). Along with Tokiko and her own Buso Renkin (the "Valkyrie Skirt," an execution scythe), Kazuki joins the fight against the homunculi and their master.

Under Nariyuki Yuiga's devoted tutelage, his classmates Rizu Ogata, Fumino Furuhashi, and Uruka Takemoto are finally pulling average test scores on their worst subjects. But time is ticking, and there is still a long way to go before the three geniuses of Ichinose Academy are ready for their upcoming university exams. Meanwhile, the girls still struggle to balance the pursuit of their dreams with their growing affections for their unsuspecting tutor. Joining them are Mafuyu Kirisu, a teacher with strong views about education and talent because of her past as a rising figure skater, and Asumi Kominami, a graduate from their school aiming to attend a national medical university. With these two additions, the group of six is livelier than ever before. Completely caught up in hilarious antics with his new friends, Yuiga finds that his last year of high school now includes a lot more than just going to class and studying. [Written by MAL Rewrite]

The second season of Tales of Zestiria the Cross.