Cinque Izumi makes a promise with his best friend Rebecca to go flower viewing during the last three days of Spring Break. However, while he is alone trying out some acrobatic moves in school, a dog appears and opens a magical portal while Cinque is in mid-air, resulting in him jumping through the portal with the dog. He arrives in the land of Flonyard, and is greeted by a beautiful girl, albeit with bestial features like dog ears and tail. The girl, who introduces herself as Princess Millhiore, requests for his assistance, which he agrees to and becomes the Princess' Hero, in order to drive away the forces of Galette which seeks to invade Biscotti.

Biscotti's army fights a losing battle with the forces of Galette until Cinque manages to hold off the enemy's offensive fighting alongside Captain Éclair Martinozzi. However, the two must join forces to confront Galette's commander and most powerful warrior, Leonmichelli Galette des Rois.

The battle ends with Biscotti's victory, but Cinque learns that Millhiore was not aware that once he was summoned to Flonyard, he cannot return home. Meanwhile, Leonmichelli's younger brother, Gaul, learns of his sister's defeat and is eager to face Cinque in combat.

Gaul's special forces, the Génoise trio, kidnaps Millhiore and he challenges Cinque to a duel. Cinque, Éclair and chief researcher Ricotta Elmar come with a plan to storm the fortress where she is being held to rescue her in time for her victory concert. Heavily outnumbered by the enemy, Cinque and Éclair manage to turn the tides when the freelance knights Brioche d'Arquien and Yukikaze Panettone come to assist them.

Cinque and Gaul's duel is interrupted by Leonmichelli who reprimands both for ruining Biscotti's victory party. Almost running out of time for Millhiore's concert, Cinque comes with a plan to return the princess to the castle for her performance.

Cinque learns from Millhiore how she used her stargazing powers to learn about him and why she chose him as her hero. Meanwhile, Leonmichelli confirms by using her own stargazing powers that an ominous fate awaits them.

Desperate to change Millhiore and Cinque's dreadful fate, Leonmichelli challenges Biscotti for another battle with each country waging their most sacred treasures on it. Millhiore reluctantly accepts the challenge, unaware of her true intentions.

The day of the battle comes and it does not take long for Millhiore to confirm her suspicions about Leonmichelli's behavior and she joins Cinque and Éclair to storm the fortress where Leonmichelli is stationed to confront her. Meanwhile, Brioche and Yukikaze feel that a strange presence is approaching.

Bearing both sacred swords, Millhiore reaches the top of the fortress to confront Leonmichelli, who trembles when she realizes that her actions are leading the princess to the same destiny she fought so much to avert, when a powerful and ominous creature appears before them.

Cinque and Millhiore manage to subdue the monster and restore the fox cub to its former self. Yukikaze offers herself to take care of it and a huge concert featuring the princess is held to celebrate the end of the hostilities between Biscotti and Gallete.

Just after Millhiore confesses her love for him, Cinque is sent back home and has no recollecions of his days at Flonyard. However, Ricotta learns that a way to make his memories return and be summoned back is possible, thanks to the possessions he left behind as a keepsake to his friends and the promise he made to them that he would indeed return. Upon regaining his memories, Cinque renews his vow to visit Flonyard again as soon as possible.

The hero of Biscotti is back and this time he is not alone, he has brought 2 new Heroes to compete in war!

The current ruler of Pastillage is jealous of those competing in the war. After she catches a glimpse of Rebecca, she is determined to make her a Knight.

Rebecca has taken to the skies and Pastillage has official joined the war. Her skill as a mage and playing video games quickly turns the tide of the battle.

With the war games over each Princess has gone back to their respective kingdoms. Sink, along with friends, are spending their time training in counter-monster skills.

Highway Bandits are ruining the lives of the people in Ayase. Nana, Vert, and Jau head out to stop the bandits but meet a much more interesting character.

A seal in a cave of monsters has been broken leaving the Heroes of old to call in the new generation.

The festival is in danger due to the abilities of an unexpected guest.

A new war between the nations is about to begin but Biscotti's Captain of the Imperial Guard is having problems that will lead Biscotti into ruin.

The monster grabs Millhiore and flees the fortress on a rampage. Cinque struggles to reach the princess before she is absorbed by the creature, while she learns that the monster is actually a fox deity cub whose body was pierced by a cursed sword.

At last Ricotta and her assistants come with a way for Cinque to return home. However, she finds that by doing so, not only he will forget all memories and experiences of his time at Flonyard, but he will never be able to come back. Upon learning of it, Cinque asks Ricotta to not tell the truth to the others, as he does not want them to send him off with a sad face.

Couverte and Sink have accidently released the Demon King from his sleep. Even with all the heroes powers combined he proves to be a formidable enemy. Only the Hero King can stop his rampage.

One on one battles continue with Becky vs. Millihiore, Rebecca vs. Hina, and Sink vs. Gaul. A wild card appears to shake the battle up even more.

With the crisis averted, the heroes return to their respective kingdoms, but when Nanami and the Genoise Trio pay a visit to Pastillage, they get into a slimy mess when some dangerous creatures break free at the castle.

The time has come for Leonmitchelle's annual challenge in which whoever defeats the princess earns the right to marry her, but this time, a new and powerful contestant who is an old friend of hers, appears as well.