Chrono's Memory - S7.E8

Transported to a secluded ruined area, Chrono cardfights Ryuzu. While battling, bits of Chrono's lost memories regarding his father slowly pop into his mind until he finally recalls the incident involving himself, Rive, and Ryuzu.

As it turns out, Rive and Ryuzu were friends who were working on creating a link between Earth and the planet Cray. One day, Chrono was brought over to a laboratory and watched an experiment in which Rive was used to open a portal to Cray. However, Rive later learned how Ryuzu wanted to sacrifice Cray for Earth's benefit. While Rive argued with him, Chrono heard a voice calling him from the Cray side of the portal. That voice belonged to Chrono Dran, and Chrono had summoned the dragon to Earth. When Ryuzu wanted to capture Chrono Dran, Rive knew at that moment what he had to do. He overloaded the system, caused the portal to explode, and destroyed the lab while protecting Chrono and Chrono Dran. While carrying the two away, Rive told Chrono to forget everything.

Back in the present time, with all of his memories retained, Chrono is more appalled with Ryuzu, who knocks him unconscious with a taser.