Rei loves exciting battles, especially when he has a strong opponent. He calls himself "The Number One Star" and is obsessed with being the number one. He gets burned up easily and is very interested in getting the ultimate treasure, The Ultimate Battle Spirits.
When he battles, he changes personality, depending on his form. His red form, Zero the Burning, is hotblooded while his white form, Zero the Silver, is more cool and serious.

Rei is an ultimate-user and Card Quester, who is seeking The Ultimate Battle Spirits. He travels through space in his ship, The Number One Star Ship. His partner is a dragon named Mugen, who turns into the card Mugendra. He is also friends with a robot named Salt, who cooks pizza.