While under the influence of Vector's Barian powers, Hart suffers from a split personality: that of a sadistic nature with a desire to destroy the Astral World, as seen when he's laughing at its inhabitants' suffering, saying that he "needs more screams" (in the dub he says he needs more energy), as that is what comforts him.[4] When he's not using his powers, he tends to act quite vulnerable, usually staying in bed, or looking down at Heartland City from the Heartland Tower, wondering why he cannot enjoy laughter like the people who attend the Heartland Fairground.

Before Hart went to live in Heartland and after he got better he was a regular kid, who loved to play and have fun. He has a very kind personality and is always trying to look out for others,especially Kite.In the anime Kite states that Hart has not been his usual self as in the past, as he used to enjoy laughter and was playful and talkative and was very kind.[3]

During the Duel when Dr. Faker is possessed by Vector, he was shown to deeply care for Kite and Yuma, as he could not bear to see them in pain and shedding tears.[5] After the Duel with Vector, Hart was fully rid of the Barian's influence (with the blank stare and bags under his eyes gone) and his personality reverted to the way it was in the past.[6]