He seems to be Yusuke Fujiwara's ace card before taking him out of his deck (because he didn't want to involve Honest in his study of Darkness), and Honest was likely his Spirit Partner.
In episode 159, Jaden Yuki found this card somewhere in the Abandoned Dorm. When this monster's spirit confronts Jaden and his friends, Jaden brandishes this card in front of the Duel Spirit and orders the Spirit to reveal himself since he knows he is not Yusuke.
In episode 160, Honest is forced to retreat back into his card after Trueman fatally wounds him. Jaden then places this card into his Deck before his Duel against Trueman. On the last turn of the Duel, "Elemental HERO Neos" attacks "Five-Headed Dragon". Jaden then sends this card from his hand to the Graveyard in order to increase the ATK of "Neos" by the ATK of "Five-Headed Dragon" until the End Phase. "Neos" then destroys "Five-Headed Dragon", winning Jaden the Duel.
In episode 176, Jaden uses this card during his Triangle Duel against Jesse Anderson and Yusuke Fujiwara. He Normal Summons this card in Attack Position. This card then attacks and destroys "Clear Cube". The latter's second effect activates, letting Yusuke Special Summon another "Clear Cube". Later "Clear Vicious Knight" (whose ATK was 3400 due to its own effect) attacks this card, but Jesse activates "The One to be Protected" to prevent this card from being destroyed and nullify the Battle Damage Jaden would take by sending "Rainbow Dragon" from his Deck to the Graveyard. Shortly after, Jesse takes equal to the ATK of "Rainbow Dragon", defeating him. After Jaden Fusion Summons "Rainbow Neos", Nightshroud claims Jaden still can't create a miracle as he activates the second effect of "Clear Vicious Knight" to increase its ATK by the ATK of "Rainbow Neos". When Yusuke tells Jaden to disappear into the World of Darkness, Jaden exploits Nightshroud's weakpoint and states to Nightshroud he was controlling Yusuke from within the latter's mind as a shadow. Due Jaden to revealing this, Nightshroud's control over Yusuke begins to weaken and he tries to take control of Yusuke by force. Jaden then activates the second effect of "Honest" to return it to his hand. This allows the spirit of "Honest" to go to Yusuke and expel out Nightshroud from Yusuke. "Rainbow Neos" then attacks "Clear Vicious Knight". Jaden then sends this card from his hand to the Graveyard in order to increase the ATK of "Rainbow Neos" by the ATK of "Clear Vicious Knight" until the End Phase. "Rainbow Neos" then destroys "Clear Vicious Knight" and wins Jaden the Duel. Yusuke then remembers everything from his past and thanks "Honest" before passing out.
This card is also shown in a flashback explained by Yusuke when he explains that he believed that bonds and friends are what brings suffering to people because his parents died and he believed they abandoned him. A younger Yusuke is shown dropping this card as he is saddened by the deaths of his parents. Later it is shown that Yusuke placed this card in a box after he gained the powers of Nightshroud and decided to remove himself from existence so that he could no long feel any more suffering in himself.
This card is also shown in a flashback explained by Jaden when he explains to Yusuke he didn't place this card in a box, so he could forget about it, but did so carefully so that the Duel Spirit would not be corrupted by the powers of darkness.
In episode 178, this card is shown in a series of flashbacks Jaden has when he tells the people trapped in the World of Darkness that the card that a Duelist bonds with is initially just a plain card without anything special, however people that a Duelist fight against and the feelings that were shared among those people as well as the memories of those Duels will be absorbed into the bonded card as it's the history of a person's efforts.