|Ryujiro Mizunuma (younger brother)|
|Anime debut||Yu-Gi-Oh! VRAINS episode 61: "Despair From Darkness"|
Kotaro Mizunuma (
Kotaro, his younger brother, Ryujiro and three others harassed a student in a shopping district. They were stopped by Takeru Homura. Ryujiro urged his brother to just beat Takeru up, but Kotaro cited that he had dangerous eyes and the group fled. Later, Ryujiro spoke about Link VRAINS and Playmaker to one of the other gang members. He was interrogated by Takeru, who was looking for information on those topics. Kotaro intervened and Takeru left. Kotaro vowed to make Takeru pay, but Ryujiro's interaction with Takeru had given him an idea.
The group kidnapped Kiku, and sent her friend, Hana to get Takeru. When Takeru appeared, they released Kiku after Takeru agreed to Duel Ryujiro, with the wager that Takeru would become their minion if he lost. Kotaro warned Takeru that his brother had competed in a National Duel tournament before. He was concerned when his brother's monsters were destroyed, but he was surprised when no damage was done.
- Yu-Gi-Oh! VRAINS episode 61: "Despair From Darkness"