Aichi goes to the card shop to buy a booster pack in the hopes of getting a Grade 3 card. When he arrives, he sees a grade-school kid, Kamui Katsuragi, convincingly defeating Izaki in a cardfight. Aichi challenges Kamui, but he refuses, noticing that Aichi is not a strong player. Then, after Kamui beats Morikawa in a cardfight, Aichi tries to buy a booster pack. Suddenly, Emi appears, and Kamui immediately falls in love with her. Before Aichi could buy a pack, Emi drags him back home while Kamui looks on, thinking that the two are boyfriend and girlfriend. Later, Aichi buys a booster pack and is pleased to find that the pack contained a Grade 3 card, Solitary Knight, Gancelot. Just then, Kamui shows up and challenges Aichi, demanding to get Emi if he beats him. Although Aichi misunderstands Kamui's intentions, he and Kamui begin their Vanguard fight.
Kamui uses powerful cards like Genocide Jack and King of Swords to quickly deal a ton of damage to Aichi, who strikes back by using his newly-acquired Solitary Knight, Gancelot. But in the end, Aichi loses to Kamui after he calls his ace card Asura Kaiser. Afterwards, Emi arrives and tries to get Aichi home, and it is then that Kamui learns that the two are actually siblings. Now, hoping to get closer to Emi, Kamui starts referring to Aichi as his "big brother", although Aichi is not exactly glad about it.
