Hiroki Moriyama is a character in the Cardfight!! Vanguard G series, first appearing in Cardfight!! Vanguard G: Stride Gate and returning in Cardfight!! Vanguard G: Z. He worked for Ryuzu Myoujin as a member of Company before the group disbanded. After the events of Stride Gate, Hiroki attends the same school as his friend and rival, Taiyou Asukawa.
Hiroki has a highly twisted sense of right and wrong due to being bullied as a child and is constantly talking about "Justice". He believes that he and the company is a hero while Chrono and his friends are evil. He is also very boastful. He can be seen as hypocritical.
When he reappears in the fourth episode of G Z, Hiroki seems to have grown out of most of the negative traits of his previous character, being more friendly and supportive, and no longer speaking of "justice" the way he used to, and seemingly no longer thinking Chrono and his friends are evil. He also seems to care more about and pay more attention to the people and things around him, as he showed concern for Taiyou, and was also aware of all his previous play styles up until that point. Otherwise, Hiroki maintains his determination to be great, and his confidence in himself.
At some point during his childhood Hiroki was being bullied by his fellow students, which caused him to turn violent. As his classmates looked on in fear, he saw the bullies crying at his feet and one of them acknowledged that Hiroki was right. This was the origin of Hiroki's "Justice" and he started violently enforcing the school's rules.
During the raid on Ryuzu's hideout, Hiroki appeared to protect the summoned units. He created an electric barrier around the perimeter and brought a bunch of robots into the room to keep Ibuki's army busy while Ryuzu and the Company gathered the Stride Force necessary to move the summoned units to another location, and was successful.
He is later seen in the room when Ryuzu is being revived into a clone body.
In GC Episode 29, Hiroki and Am went to the United Sanctuary Branch to fight Ren and then destroy the Branch. Since AL4 wasn't around, Taiyou fought him instead. During the fight, Hiroki continually called Taiyou weak and wouldn't shut up about his "justice" and how the righteous will always win and can do whatever they want. This reminded Taiyou of his former self and how United Sanctuary used to be, which made Taiyou determined to win because he didn't want that way of thinking to come back to the United Sanctuary Branch. However, Hiroki eventually won by using his trump card's Quadruple Drive ability. Am Chouno then summoned one of the Zodiac Time Beasts and used its power to destroy the building.
At the end of the episode, Hiroki and Am are seen walking when Am trips. Hiroki looks back, calls Am a disappointment, and keeps walking.
In the fourth episode of G Z, Hiroki comes back to comfort Taiyou and tell him Chrono will be alright. He then walks him home, and after he tells Taiyou how he is the best person for Taiyou's team for next year's Under 20, he watches as Valeos appears and challenges Taiyou to a fight. He is there to witness the fight, supporting Taiyou all the way through it and also giving a commentary on Taiyou's fight and exclaiming on how his play style has grown, and is present all the way until the fight ends, and Taiyou is cast into Relics by Valeos.