Gustav is Vincent Bari's partner. Their relationship mirrors that of a stern father and a rebellious son, yet Bari seems to respect Gustav, albeit somewhat reluctantly, due to his vast knowledge.
Even though Gustav often acts as a disapproving father figure, he commends Bari when Bari sacrifices himself to save Gash and the others. He states that although Bari did not become the king of the mamodo world, he has grown into a man powerful enough to challenge even the king. Gustav silently sheds tears and bids farewell to Bari, who also cries, promising never to forget him.
After Bari's book was burned, it appears that Gustav returned home. He was later seen fervently praying for Zatch's victory against Clear.
(Source: Zatch Bell! Wiki)










