Cardfight!! Vanguard - 7x12 - Season 7, Episode 12- Followmy.tv

Shin tells Chrono about his past with Rive. Back then, Shin was part of Team Nippon along with Mark Whiting and Rive, who was also the team's mentor. Together, they won the national Vanguard tournament and were invited to the world championship. Around the same time, Rive was also spending time with Ryuzu, which Shin did not like because it was taking time away from training. One day, Shin met Ryuzu and had a cardfight with him; if Shin won, then Ryuzu would not be allowed to see Rive. Although Shin won, Rive still kept meeting with Ryuzu. Eventually, Shin realized the likely reason why Rive kept seeing Ryuzu: they both agreed on and pursued the idea that Vanguard can be used to make the world a better place. Rive tells Shin about the existence of the Gear Chronicle clan and said that it was the key to change the world, which was the last memory Shin had of him.