The story follows three 15-year-old boys who go to a prestigious horse racing academy to become jockeys. The three-year academy is 10 to 20 times harder to enter than most schools, and whoever wishes to enter must pass an academic, physical, and fitness test. Formerly a member of an idol group winning fans and fame, Yuu Arimura sets out to meet what his heart desires after becoming enamored with horse racing. Having grown up on an island, Shun Kanami has always yearned to ride with horses. Amane Grace was born in England and is lost in the path his parents have set for him, but he still takes on his dream.

Winter is approaching, and Myne—now an apprentice priestess—must prepare for her stay at the church and the upcoming Dedication Ceremony. However, due to her immense knowledge and extraordinary amount of mana, she has garnered the attention of many dangerous people, who are willing to do anything to get their hands on Myne. To keep her safe, the Head Priest assigns Myne a bodyguard and advises her to be adopted by a noble, a decision that will force her to leave her family behind. As Myne is opposed to the idea, the Head Priest gives her an ultimatum: she can be with her family until she turns 10, but if she is deemed too unstable, she will immediately be dealt with. Placed in a tough position, Myne is uncertain about her future. Despite the twists that may lie ahead, she will do whatever she can to protect those that she loves—even if it means giving up on her dream.

When Demon Queen Echidna begins her invasion of the human realm, the people turn to the hero Leo Demonheart to protect them. Blessed with insurmountable power, Leo easily repels Echidna's army, thereby saving the world. But instead of gratitude or admiration, Leo is met with disdain and scorn from his fellow humans, who fear his overwhelming strength and believe that it may eventually cause humanity's demise. Banished from the kingdom he once called home, Leo wanders aimlessly throughout the land until, one day, he hears rumors of Echidna's efforts to rebuild her army. Hoping that demonkind might accept him as an ally, he returns to the demon queen's castle and offers Echidna his help. Naturally, Echidna immediately rejects him. Still, not all hope is lost, as Leo manages to convince Echidna's four generals to let him secretly work under their supervision. Donning the identity of a masked dark knight named Onyx, Leo solves the demon army's problems one by one—gradually improving the quality of life around the castle. Above all else, however, Leo wants to accomplish one goal: to learn why Echidna started the war in the first place.