The Emperor of Vandole once used the power of Mana for evil purposes, but Vandole's evil purpose were stopped by the Knights of Gemma who guarded the Tree of Mana. The Gemma Knights joined hands with the Mana family, the keepers of the Tree of Mana, to fight a long hard battle. Finally, they were able to restore peace to the world.
In the modern day, a Gemma Knight by the name of Hasim who works for Bogard is escorting Fuji. However, he is fatally wounded from trying to protect her from monsters, though before he dies. He ask Sumo to bring the girl to see Bogard. After meeting him, he mentions that Fuji is the key to win this time against Glaive Empire.
After Fuji's kidnap in Wendel and brought inside the airship, it flies to the west. Sumo goes after her, and after coming out of Gaia Pass. Borgard catches up with him and tells him that Glaive's Airship is refueling at a lake up north. They both board the airship and locates Fuji within it, but end up being thrown off the airship and both of them ends up separated.
Sumo later ends up in Ish, wakes up next to Borgard who's bedridden since his back is broken and won't be able to move for a while. He is distressed to hear other places are being attacked, but kept saying there is a boy named Sumo who will come and save everyone. Sumo loses his confidence with himself, claiming he is not a Gemma Knight. Bogard tries to talk some sense to him, but Sumo does not let him. He tells Bogard that he is a Gemma Knight, and he should do it. Bogard angrily tells Sumo to get out of the house, which Sumo does.
Sumo revisits him before leaving town, and Bogard warns him it'll be a perilous journey. Julius got the power of Mana, and the only match against it is a knight wielding the legendary sword Excalibur. This is how the Gemma Knights defeated the evil power of Vandole.
After much searching and adventuring, Sumo finds the rusty sword instead of Excalibur. Disappointed, he returns to Cibba in Lorim. He tells him that the only thing left to do is to reveal the Dime Tower in the Desert of Crystal. Sumo asked him how, and reply that the sword will help him. He should use it in the Cave of Ruins. Sumo is surprise to hear that the rusty sword had such great power. Cibba tells him that the legendary sword only shows its real power when it approves the wielder, stating that if he's a real Knight of Gemma. It will help him.
After passing through the Dime Tower and the Temple of Mana, Sumo reaches the Mana Shrine. Sumo meets Fuji's Mother before facing Julius. She tells him that he has become a great Knight of Gemma, and transforms the rusty sword into Excalibur before disappearing.
Sumo uses the Excalibur against Julius, and with it bring him down and peace returns to the world. Fuji decides to become the last Mana Tree, and Sumo ends up the last of the Gemma Knights, and his sole task is to protect the Mana Tree.
There are only three known members:
- Sumo: The last of the Gemma Knights, task in protecting the last Mana Tree.
- Hasim: A Gemma Knight task in escorting Fuji to Bogard, he's fatally wounded from trying to protect her from monsters, though before he dies. He ask Sumo to bring the girl to see Bogard in his place.
- Bogard: A mighty warrior of the Gemma Knights, he assist Sumo in his quest to save the captive Fuji from Glaive Empire's hands. He ends up bedridden, but doesn't loses his faith in Sumo that he'll be able to restore the peace onto the world.