|Appearance||Tales of Hearts|
|Height||6'4" / 193 cm|
|Weight||170 lbs / 77 kg|
|Weapon||Soma Vex (Katars)|
|Japanese Voice Actor||Hozumi Gouda|
|Character Designer||Mutsumi Inomata|
Kuzite is a machine with an artificial Spiria Nexus, giving him some semblance of emotions. He is a mechanical guardian knight who had been in operation more than 2,000 years ago. Created to protect Lithia Spodumene, he has a heartless-looking face and considers things from a coldly logical perspective. He possesses the Soma Vex (ヴェックス Vekkusu?), which also gives him extra arms at his back.
At the beginning of the story, he is found abandoned and not functioning in an enemy base. After the party fights Kornerupine and appears to be cornered by xerom-infected soldiers, he appears to help protect Kohaku Hearts with Ines Lorenzen while Kor Meteor, Hisui Hearts, and Beryl Benito escape. Kor, Hisui, and Beryl then encounter Kunzite on their way to Straga to meet with Ines and Kohaku, and Kunzite joins them. The party is wary of Kunzite, but Kor decides to trust him.
Kunzite abandons the group shortly before reaching Straga, leaving the rest to deal with a sudden monster ambush. The party encounters Kunzite again at Straga, where he learns Kohaku is the vessel that contains his mistress, Lithia, who he had been searching for. He is displeased to find that with Kohaku's Spirune shattered Lithia cannot be revived, and demands to know who caused it. Hisui lies and claims Chalcedony Akerman is at fault, as he was in possession of a Spirune fragment. Thus, Kunzite agrees to join the party and help them retrieve the fragment from Chalcedony.
Later, after they exit the Straga sewers, Kor lets slip that he was the one who caused Kohaku's Spirune to shatter into pieces. Kunzite is enraged that he was lied to and is set on killing Kor, swatting Kohaku aside when she tries to stop him. After the fight, Hisui wants Kor to finish Kunzite, but Kor refuses, saying that Kunzite has every right to be angry at him. Kohaku interjects and explains it was not really Kor's fault after all. She and Lithia willingly caused the Spirune to break to protect Lithia herself. Kunzite agrees to continue traveling with them in order to recover the rest of Kohaku's Spirune.
As the journey continues, Kunzite eventually begins humanizing, indicating his Spiria, though artificial, is growing stronger. Lithia encourages this development. At the end, when Creed Graphite is dealt with and Lithia is dying, Hisui prompts Kunzite to remember an ordeal Clinoseraph once put Lithia through. He tortured her by endlessly replaying the day of Minera's calcification. Kunzite realizes that he should be able to manipulate time within his Spiria as well. If Lithia were to enter his Spiria Nexus, she would be able to live for as long as Kunzite's mechanical body holds out, which is far longer than a human. Doing this would mean that Kunzite would also have to enter hibernation, but it is a sacrifice Kunzite is willing to make. Lithia agrees, and Kunzite vows to protect Lithia. The two of them then go to sleep and dream of the day that Minera revives, never losing the bond they share with the others.
- Kunzite is named after the gemstone of the same name, kunzite.