Aurum is unrelated to Ib and Ningirsu, however he's always with them in their fight against whatever. His card text reads this (Once again, using the OCG version):

Alternate forms he takes:

- Mekk-Knight Avrum

- Crusadia Maximus

- Crusadia Equimax

- Mekk-Knight Crusadia Astram

An honest youth who has equipped himself with the remains of  Mekkstrosities.
Having long since admired the "Star Hero" [Mekk-Knight Blue Sky, a character that isn't relevant as of now since he appears later on] told in stories around the Celestial Forest since ancient times, he accepted Fairy Lees' request, and set out on a journey to release the Seven Star Relics [World Legacies] with his comrades who have also been gifted by the light.
"Starlight Hero, Raise Your Sword and Gather the Light, You Must Vanquish the Great Darkness"

Aurum seems to be in love with Ib or something, shown through some of the artwork. Anyhow, his voice would be something like uh... Just a regular teen I suppose. To make this more interesting, even though it doesn't show it through the card art, I'm just going to say he's a bit cocky, however he deeply cares about his friends and such, always willing to fight with/for them.

His flavor text (The Japanese Version, because the American version is literally just, "Check THIS out!") for when he becomes Mekk-Knight Avram:

The hero [Mekk-Knight Blue Sky] who defends the light of the stars
Must destroy the darkness [Knightmares] of the illusory world
And entrust his power to the chosen one [Aurum].
The will inherited by the chalice of the stars will become a new key
And become the sword that cuts down darkness.